diff mbox

[1/4] ARM: OMAP2+: omap_hwmod: Introduce ti, no-init dt property

Message ID 1425561211-31003-2-git-send-email-d-gerlach@ti.com
State New, archived
Headers show

Commit Message

Dave Gerlach March 5, 2015, 1:13 p.m. UTC
Introduce a dt property, ti,no-init, that prevents hwmod initialization.
Even if a dt node is marked as disabled, hwmod still at least enables
the hwmod and programs the sysconfig before attempting to idle it at
boot. If an IP has been disabled by the hardware configuration on a
platform, this will cause a hang due to writing to inactive registers.
This property prevents that from happening by marking the hwmod as
_HWMOD_STATE_DISABLED during init.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
---
 Documentation/devicetree/bindings/arm/omap/omap.txt | 2 ++
 arch/arm/mach-omap2/omap_hwmod.c                    | 7 ++++++-
 arch/arm/mach-omap2/omap_hwmod.h                    | 4 ++++
 3 files changed, 12 insertions(+), 1 deletion(-)

Comments

Paul Walmsley March 5, 2015, 6:16 p.m. UTC | #1
On Thu, 5 Mar 2015, Dave Gerlach wrote:

> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
> Even if a dt node is marked as disabled, hwmod still at least enables
> the hwmod and programs the sysconfig before attempting to idle it at
> boot. If an IP has been disabled by the hardware configuration on a
> platform, this will cause a hang due to writing to inactive registers.
> This property prevents that from happening by marking the hwmod as
> _HWMOD_STATE_DISABLED during init.

I'm kind of wondering if hwmod should even touch a device if it's marked 
as disabled in the DT.  Tony, what do you think?


- Paul
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Tony Lindgren March 5, 2015, 6:49 p.m. UTC | #2
* Paul Walmsley <paul@pwsan.com> [150305 10:16]:
> On Thu, 5 Mar 2015, Dave Gerlach wrote:
> 
> > Introduce a dt property, ti,no-init, that prevents hwmod initialization.
> > Even if a dt node is marked as disabled, hwmod still at least enables
> > the hwmod and programs the sysconfig before attempting to idle it at
> > boot. If an IP has been disabled by the hardware configuration on a
> > platform, this will cause a hang due to writing to inactive registers.
> > This property prevents that from happening by marking the hwmod as
> > _HWMOD_STATE_DISABLED during init.
> 
> I'm kind of wondering if hwmod should even touch a device if it's marked 
> as disabled in the DT.  Tony, what do you think?

Well nothing happens if a device is status = "disabled". No dev entry
gets created for it at all and hwmod won't have any data for the device
populated. The only way hwmod code could see that device if the device
gets it's data from the legacy omap_hwmod_*_data.c instead of DT.

So maybe the comments in the $subject patch are incorrect for that?

What we really should have is also status = "incomplete" where the
dev entry gets created, but the driver never probes. This would be for
devices that are still there within the SoC, but not pinned out for
the board in question.

We still may need also ti,no-init too for devices that we don't want
hwmod to do anything with, for example in secure mode if some blocks
are not available to Linux at all. I believe that's what's going on with
n900 crypto accelerators for example.

Regards,

Tony
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Dave Gerlach March 5, 2015, 7:47 p.m. UTC | #3
On 03/05/2015 12:49 PM, Tony Lindgren wrote:
> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>
>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>> the hwmod and programs the sysconfig before attempting to idle it at
>>> boot. If an IP has been disabled by the hardware configuration on a
>>> platform, this will cause a hang due to writing to inactive registers.
>>> This property prevents that from happening by marking the hwmod as
>>> _HWMOD_STATE_DISABLED during init.
>>
>> I'm kind of wondering if hwmod should even touch a device if it's marked 
>> as disabled in the DT.  Tony, what do you think?
> 
> Well nothing happens if a device is status = "disabled". No dev entry
> gets created for it at all and hwmod won't have any data for the device
> populated. The only way hwmod code could see that device if the device
> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
> 

We still need this for the sysconfig programming, correct? hwmod programs that
regardless of dt status and then idles the IP, which is why I needed the
ti,no-init for the epos evm. It isn't just a matter of we shouldnt write to it
because we don't want to use it; we can't write to it because the module is held
off so it causes an external abort if we do.

Regards,
Dave

> So maybe the comments in the $subject patch are incorrect for that?
> 
> What we really should have is also status = "incomplete" where the
> dev entry gets created, but the driver never probes. This would be for
> devices that are still there within the SoC, but not pinned out for
> the board in question.
> 
> We still may need also ti,no-init too for devices that we don't want
> hwmod to do anything with, for example in secure mode if some blocks
> are not available to Linux at all. I believe that's what's going on with
> n900 crypto accelerators for example.
> 
> Regards,
> 
> Tony
> 

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Tony Lindgren March 5, 2015, 8:17 p.m. UTC | #4
* Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
> > * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
> >> On Thu, 5 Mar 2015, Dave Gerlach wrote:
> >>
> >>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
> >>> Even if a dt node is marked as disabled, hwmod still at least enables
> >>> the hwmod and programs the sysconfig before attempting to idle it at
> >>> boot. If an IP has been disabled by the hardware configuration on a
> >>> platform, this will cause a hang due to writing to inactive registers.
> >>> This property prevents that from happening by marking the hwmod as
> >>> _HWMOD_STATE_DISABLED during init.
> >>
> >> I'm kind of wondering if hwmod should even touch a device if it's marked 
> >> as disabled in the DT.  Tony, what do you think?
> > 
> > Well nothing happens if a device is status = "disabled". No dev entry
> > gets created for it at all and hwmod won't have any data for the device
> > populated. The only way hwmod code could see that device if the device
> > gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
> > 
> 
> We still need this for the sysconfig programming, correct? hwmod programs that
> regardless of dt status and then idles the IP,

Well hwmod does not even know about the IP IO addresses if it's marked
with status = "disabled".. Which IP are you having problems with?

> which is why I needed the ti,no-init for the epos evm. It isn't just a
> matter of we shouldnt write to it because we don't want to use it; we
> can't write to it because the module is held off so it causes an
> external abort if we do.

Well hard to say not knowing which module this is.. Pretty much all
the modules have drivers and the driver just does pm_runtime_get()
on it?

Regards,

Tony
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Tony Lindgren March 6, 2015, 12:41 a.m. UTC | #5
* Tony Lindgren <tony@atomide.com> [150305 12:24]:
> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
> > On 03/05/2015 12:49 PM, Tony Lindgren wrote:
> > > * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
> > >> On Thu, 5 Mar 2015, Dave Gerlach wrote:
> > >>
> > >>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
> > >>> Even if a dt node is marked as disabled, hwmod still at least enables
> > >>> the hwmod and programs the sysconfig before attempting to idle it at
> > >>> boot. If an IP has been disabled by the hardware configuration on a
> > >>> platform, this will cause a hang due to writing to inactive registers.
> > >>> This property prevents that from happening by marking the hwmod as
> > >>> _HWMOD_STATE_DISABLED during init.
> > >>
> > >> I'm kind of wondering if hwmod should even touch a device if it's marked 
> > >> as disabled in the DT.  Tony, what do you think?
> > > 
> > > Well nothing happens if a device is status = "disabled". No dev entry
> > > gets created for it at all and hwmod won't have any data for the device
> > > populated. The only way hwmod code could see that device if the device
> > > gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
> > > 
> > 
> > We still need this for the sysconfig programming, correct? hwmod programs that
> > regardless of dt status and then idles the IP,
> 
> Well hwmod does not even know about the IP IO addresses if it's marked
> with status = "disabled".. Which IP are you having problems with?
> 
> > which is why I needed the ti,no-init for the epos evm. It isn't just a
> > matter of we shouldnt write to it because we don't want to use it; we
> > can't write to it because the module is held off so it causes an
> > external abort if we do.
> 
> Well hard to say not knowing which module this is.. Pretty much all
> the modules have drivers and the driver just does pm_runtime_get()
> on it?

Heh OK this thread is about the RTC driver, so I assume that's the
problem :) So if you set the rtc to status = "disabled" how can the
hwmod code do anything as AFAIK it won't even get the rtc IO address?

Or am I missing something here?

Regards,

Tony
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Dave Gerlach March 6, 2015, 5:28 p.m. UTC | #6
On 03/05/2015 06:41 PM, Tony Lindgren wrote:
> * Tony Lindgren <tony@atomide.com> [150305 12:24]:
>> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
>>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
>>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>>>>
>>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>>>>> the hwmod and programs the sysconfig before attempting to idle it at
>>>>>> boot. If an IP has been disabled by the hardware configuration on a
>>>>>> platform, this will cause a hang due to writing to inactive registers.
>>>>>> This property prevents that from happening by marking the hwmod as
>>>>>> _HWMOD_STATE_DISABLED during init.
>>>>>
>>>>> I'm kind of wondering if hwmod should even touch a device if it's marked 
>>>>> as disabled in the DT.  Tony, what do you think?
>>>>
>>>> Well nothing happens if a device is status = "disabled". No dev entry
>>>> gets created for it at all and hwmod won't have any data for the device
>>>> populated. The only way hwmod code could see that device if the device
>>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
>>>>
>>>
>>> We still need this for the sysconfig programming, correct? hwmod programs that
>>> regardless of dt status and then idles the IP,
>>
>> Well hwmod does not even know about the IP IO addresses if it's marked
>> with status = "disabled".. Which IP are you having problems with?
>>
>>> which is why I needed the ti,no-init for the epos evm. It isn't just a
>>> matter of we shouldnt write to it because we don't want to use it; we
>>> can't write to it because the module is held off so it causes an
>>> external abort if we do.
>>
>> Well hard to say not knowing which module this is.. Pretty much all
>> the modules have drivers and the driver just does pm_runtime_get()
>> on it?
> 
> Heh OK this thread is about the RTC driver, so I assume that's the
> problem :) So if you set the rtc to status = "disabled" how can the
> hwmod code do anything as AFAIK it won't even get the rtc IO address?
> 
> Or am I missing something here?

Perhaps I am mistaken, but from what I understand, all hwmods have _init and
_setup called on them, and all hwmods read the IO address regardless of DT
status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
which calls _enable for the hwmod, and this calls both _enable_sysc and
_update_sysc_cache which touch the sysconfig register of the IP.

Normally this is fine regardless of whether or not we are using an IP because
the module will wake up for a moment, have it's sysc programmed, and then be put
back to sleep later, potentially never to be woken again if we bind no driver
for it, which is fine for 99% of cases. In the case of am43x epos evm, you can
take the same piece of silicon that will boot happily on the gp evm with the rtc
hwmod in place and it will hang during boot on the epos evm because the board
uses a pin to hold the RTC IP in reset. There is no way to detect this in
software, the module can be turned on as normal using the clk_ctrl, but if you
touch any of the IP registers you get an abort.

So we need to prevent this from happening but of course we can't selectively
choose when the rtc hwmod gets added based on which board we are using so it
seemed a DT flag was appropriate to indicate that we do not want to init the rtc
IP at all only on this board.

Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
fails booting with an imprecise abort.

Regards,
Dave

> 
> Regards,
> 
> Tony
> 

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Tony Lindgren March 6, 2015, 5:45 p.m. UTC | #7
* Dave Gerlach <d-gerlach@ti.com> [150306 09:28]:
> On 03/05/2015 06:41 PM, Tony Lindgren wrote:
> > * Tony Lindgren <tony@atomide.com> [150305 12:24]:
> >> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
> >>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
> >>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
> >>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
> >>>>>
> >>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
> >>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
> >>>>>> the hwmod and programs the sysconfig before attempting to idle it at
> >>>>>> boot. If an IP has been disabled by the hardware configuration on a
> >>>>>> platform, this will cause a hang due to writing to inactive registers.
> >>>>>> This property prevents that from happening by marking the hwmod as
> >>>>>> _HWMOD_STATE_DISABLED during init.
> >>>>>
> >>>>> I'm kind of wondering if hwmod should even touch a device if it's marked 
> >>>>> as disabled in the DT.  Tony, what do you think?
> >>>>
> >>>> Well nothing happens if a device is status = "disabled". No dev entry
> >>>> gets created for it at all and hwmod won't have any data for the device
> >>>> populated. The only way hwmod code could see that device if the device
> >>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
> >>>>
> >>>
> >>> We still need this for the sysconfig programming, correct? hwmod programs that
> >>> regardless of dt status and then idles the IP,
> >>
> >> Well hwmod does not even know about the IP IO addresses if it's marked
> >> with status = "disabled".. Which IP are you having problems with?
> >>
> >>> which is why I needed the ti,no-init for the epos evm. It isn't just a
> >>> matter of we shouldnt write to it because we don't want to use it; we
> >>> can't write to it because the module is held off so it causes an
> >>> external abort if we do.
> >>
> >> Well hard to say not knowing which module this is.. Pretty much all
> >> the modules have drivers and the driver just does pm_runtime_get()
> >> on it?
> > 
> > Heh OK this thread is about the RTC driver, so I assume that's the
> > problem :) So if you set the rtc to status = "disabled" how can the
> > hwmod code do anything as AFAIK it won't even get the rtc IO address?
> > 
> > Or am I missing something here?
> 
> Perhaps I am mistaken, but from what I understand, all hwmods have _init and
> _setup called on them, and all hwmods read the IO address regardless of DT
> status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
> which calls _enable for the hwmod, and this calls both _enable_sysc and
> _update_sysc_cache which touch the sysconfig register of the IP.

Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(),
sorry. Looks like the hwmod IO address data does get populated even
for status = "disabled" although the dev entry won't get created and
omap_device_build_from_dt() never gets called.

> Normally this is fine regardless of whether or not we are using an IP because
> the module will wake up for a moment, have it's sysc programmed, and then be put
> back to sleep later, potentially never to be woken again if we bind no driver
> for it, which is fine for 99% of cases. In the case of am43x epos evm, you can
> take the same piece of silicon that will boot happily on the gp evm with the rtc
> hwmod in place and it will hang during boot on the epos evm because the board
> uses a pin to hold the RTC IP in reset. There is no way to detect this in
> software, the module can be turned on as normal using the clk_ctrl, but if you
> touch any of the IP registers you get an abort.

OK sounds like some dts property is needed to signal this.
 
> So we need to prevent this from happening but of course we can't selectively
> choose when the rtc hwmod gets added based on which board we are using so it
> seemed a DT flag was appropriate to indicate that we do not want to init the rtc
> IP at all only on this board.
> 
> Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
> fails booting with an imprecise abort.

OK thanks for explaining it. I'm fine with this patch, Paul may have
other issues. The other option would be to use status = "disabled" to
not touch the device at all like Paul suggested. I wonder if that's
going to break PM on some devices though..

Regards,

Tony
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Dave Gerlach March 10, 2015, 4:12 p.m. UTC | #8
Tony,
On 03/06/2015 11:45 AM, Tony Lindgren wrote:
> * Dave Gerlach <d-gerlach@ti.com> [150306 09:28]:
>> On 03/05/2015 06:41 PM, Tony Lindgren wrote:
>>> * Tony Lindgren <tony@atomide.com> [150305 12:24]:
>>>> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
>>>>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
>>>>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>>>>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>>>>>>
>>>>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>>>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>>>>>>> the hwmod and programs the sysconfig before attempting to idle it at
>>>>>>>> boot. If an IP has been disabled by the hardware configuration on a
>>>>>>>> platform, this will cause a hang due to writing to inactive registers.
>>>>>>>> This property prevents that from happening by marking the hwmod as
>>>>>>>> _HWMOD_STATE_DISABLED during init.
>>>>>>>
>>>>>>> I'm kind of wondering if hwmod should even touch a device if it's marked 
>>>>>>> as disabled in the DT.  Tony, what do you think?
>>>>>>
>>>>>> Well nothing happens if a device is status = "disabled". No dev entry
>>>>>> gets created for it at all and hwmod won't have any data for the device
>>>>>> populated. The only way hwmod code could see that device if the device
>>>>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
>>>>>>
>>>>>
>>>>> We still need this for the sysconfig programming, correct? hwmod programs that
>>>>> regardless of dt status and then idles the IP,
>>>>
>>>> Well hwmod does not even know about the IP IO addresses if it's marked
>>>> with status = "disabled".. Which IP are you having problems with?
>>>>
>>>>> which is why I needed the ti,no-init for the epos evm. It isn't just a
>>>>> matter of we shouldnt write to it because we don't want to use it; we
>>>>> can't write to it because the module is held off so it causes an
>>>>> external abort if we do.
>>>>
>>>> Well hard to say not knowing which module this is.. Pretty much all
>>>> the modules have drivers and the driver just does pm_runtime_get()
>>>> on it?
>>>
>>> Heh OK this thread is about the RTC driver, so I assume that's the
>>> problem :) So if you set the rtc to status = "disabled" how can the
>>> hwmod code do anything as AFAIK it won't even get the rtc IO address?
>>>
>>> Or am I missing something here?
>>
>> Perhaps I am mistaken, but from what I understand, all hwmods have _init and
>> _setup called on them, and all hwmods read the IO address regardless of DT
>> status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
>> which calls _enable for the hwmod, and this calls both _enable_sysc and
>> _update_sysc_cache which touch the sysconfig register of the IP.
> 
> Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(),
> sorry. Looks like the hwmod IO address data does get populated even
> for status = "disabled" although the dev entry won't get created and
> omap_device_build_from_dt() never gets called.
> 
>> Normally this is fine regardless of whether or not we are using an IP because
>> the module will wake up for a moment, have it's sysc programmed, and then be put
>> back to sleep later, potentially never to be woken again if we bind no driver
>> for it, which is fine for 99% of cases. In the case of am43x epos evm, you can
>> take the same piece of silicon that will boot happily on the gp evm with the rtc
>> hwmod in place and it will hang during boot on the epos evm because the board
>> uses a pin to hold the RTC IP in reset. There is no way to detect this in
>> software, the module can be turned on as normal using the clk_ctrl, but if you
>> touch any of the IP registers you get an abort.
> 
> OK sounds like some dts property is needed to signal this.
>  
>> So we need to prevent this from happening but of course we can't selectively
>> choose when the rtc hwmod gets added based on which board we are using so it
>> seemed a DT flag was appropriate to indicate that we do not want to init the rtc
>> IP at all only on this board.
>>
>> Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
>> fails booting with an imprecise abort.
> 
> OK thanks for explaining it. I'm fine with this patch, Paul may have
> other issues. The other option would be to use status = "disabled" to
> not touch the device at all like Paul suggested. I wonder if that's
> going to break PM on some devices though..

Well the initial programming of the SYSCONFIG register is pretty important for
certain modules, just take AM33xx USB hwmod for example.

If no USB driver is bound even just letting omap_device idle it using the USB_
CLKCTRL in the PRCM after no driver gets bound will not work properly, because
the USB on am33xx expects it's SYSCONFIG STANDBY_MODE to be software supervised,
the default state (SMART_STANDBY) does not let the IP go into standby so the IP
gets stuck in a partially off state but does not actually shut down as expected.

So I don't think we can change this without consequences elsewhere.

Regards,
Dave

> 
> Regards,
> 
> Tony
> 

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Grygorii Strashko March 10, 2015, 5:36 p.m. UTC | #9
Hi Dave,

On 03/06/2015 07:45 PM, Tony Lindgren wrote:
> * Dave Gerlach <d-gerlach@ti.com> [150306 09:28]:
>> On 03/05/2015 06:41 PM, Tony Lindgren wrote:
>>> * Tony Lindgren <tony@atomide.com> [150305 12:24]:
>>>> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
>>>>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
>>>>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>>>>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>>>>>>
>>>>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>>>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>>>>>>> the hwmod and programs the sysconfig before attempting to idle it at
>>>>>>>> boot. If an IP has been disabled by the hardware configuration on a
>>>>>>>> platform, this will cause a hang due to writing to inactive registers.
>>>>>>>> This property prevents that from happening by marking the hwmod as
>>>>>>>> _HWMOD_STATE_DISABLED during init.
>>>>>>>
>>>>>>> I'm kind of wondering if hwmod should even touch a device if it's marked
>>>>>>> as disabled in the DT.  Tony, what do you think?
>>>>>>
>>>>>> Well nothing happens if a device is status = "disabled". No dev entry
>>>>>> gets created for it at all and hwmod won't have any data for the device
>>>>>> populated. The only way hwmod code could see that device if the device
>>>>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
>>>>>>
>>>>>
>>>>> We still need this for the sysconfig programming, correct? hwmod programs that
>>>>> regardless of dt status and then idles the IP,
>>>>
>>>> Well hwmod does not even know about the IP IO addresses if it's marked
>>>> with status = "disabled".. Which IP are you having problems with?
>>>>
>>>>> which is why I needed the ti,no-init for the epos evm. It isn't just a
>>>>> matter of we shouldnt write to it because we don't want to use it; we
>>>>> can't write to it because the module is held off so it causes an
>>>>> external abort if we do.
>>>>
>>>> Well hard to say not knowing which module this is.. Pretty much all
>>>> the modules have drivers and the driver just does pm_runtime_get()
>>>> on it?
>>>
>>> Heh OK this thread is about the RTC driver, so I assume that's the
>>> problem :) So if you set the rtc to status = "disabled" how can the
>>> hwmod code do anything as AFAIK it won't even get the rtc IO address?
>>>
>>> Or am I missing something here?
>>
>> Perhaps I am mistaken, but from what I understand, all hwmods have _init and
>> _setup called on them, and all hwmods read the IO address regardless of DT
>> status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
>> which calls _enable for the hwmod, and this calls both _enable_sysc and
>> _update_sysc_cache which touch the sysconfig register of the IP.
> 
> Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(),
> sorry. Looks like the hwmod IO address data does get populated even
> for status = "disabled" although the dev entry won't get created and
> omap_device_build_from_dt() never gets called.
> 
>> Normally this is fine regardless of whether or not we are using an IP because
>> the module will wake up for a moment, have it's sysc programmed, and then be put
>> back to sleep later, potentially never to be woken again if we bind no driver
>> for it, which is fine for 99% of cases. In the case of am43x epos evm, you can
>> take the same piece of silicon that will boot happily on the gp evm with the rtc
>> hwmod in place and it will hang during boot on the epos evm because the board
>> uses a pin to hold the RTC IP in reset. There is no way to detect this in
>> software, the module can be turned on as normal using the clk_ctrl, but if you
>> touch any of the IP registers you get an abort.
> 
> OK sounds like some dts property is needed to signal this.

As I understand, there is device "RTC" and this device has status 'disabled',
so there is reasonable question why do we need to touch it at all?
The HWMOD is some kind of SoC description, which was needed before DT.
Now with DT in place it seems unreasonable to touch any IP block which:
- are not defined in DT
- has status 'disabled'.
in above cases the u-boot has to dial with IP block if it's invisible for Kernel.

The HWMOD framework intended to reset and put in some predefined states IPs which are
visible for the Kernel, so then proper driver can start working with IP or IP will be
kept in some low-power state if there is no driver.

Such kind of changes really confused :(, because when I'm looking on DT and see - status='disabled'
I suppose that such IP will not be touched by Kernel. But it's NOT really 'disabled'.
It's kinda 'partially disabled' or 'not present' or 'unused' ..
(if someone will decide to continue with such approach - it could be more
useful to define new value for 'status' parameter :P).
Also, just imaging that OMAP kernel is used with Xen as DomU and how hard will
it be to find and cut off all such tricks :( 

Did I miss something?

>   
>> So we need to prevent this from happening but of course we can't selectively
>> choose when the rtc hwmod gets added based on which board we are using so it
>> seemed a DT flag was appropriate to indicate that we do not want to init the rtc
>> IP at all only on this board.
>>
>> Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
>> fails booting with an imprecise abort.
> 
> OK thanks for explaining it. I'm fine with this patch, Paul may have
> other issues. The other option would be to use status = "disabled" to
> not touch the device at all like Paul suggested. I wonder if that's
> going to break PM on some devices though..
> 

Regards,
-grygorii

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Dave Gerlach March 10, 2015, 5:59 p.m. UTC | #10
Grygorii,
On 03/10/2015 12:36 PM, Grygorii Strashko wrote:
> Hi Dave,
> 
> On 03/06/2015 07:45 PM, Tony Lindgren wrote:
>> * Dave Gerlach <d-gerlach@ti.com> [150306 09:28]:
>>> On 03/05/2015 06:41 PM, Tony Lindgren wrote:
>>>> * Tony Lindgren <tony@atomide.com> [150305 12:24]:
>>>>> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
>>>>>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
>>>>>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>>>>>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>>>>>>>
>>>>>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>>>>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>>>>>>>> the hwmod and programs the sysconfig before attempting to idle it at
>>>>>>>>> boot. If an IP has been disabled by the hardware configuration on a
>>>>>>>>> platform, this will cause a hang due to writing to inactive registers.
>>>>>>>>> This property prevents that from happening by marking the hwmod as
>>>>>>>>> _HWMOD_STATE_DISABLED during init.
>>>>>>>>
>>>>>>>> I'm kind of wondering if hwmod should even touch a device if it's marked
>>>>>>>> as disabled in the DT.  Tony, what do you think?
>>>>>>>
>>>>>>> Well nothing happens if a device is status = "disabled". No dev entry
>>>>>>> gets created for it at all and hwmod won't have any data for the device
>>>>>>> populated. The only way hwmod code could see that device if the device
>>>>>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
>>>>>>>
>>>>>>
>>>>>> We still need this for the sysconfig programming, correct? hwmod programs that
>>>>>> regardless of dt status and then idles the IP,
>>>>>
>>>>> Well hwmod does not even know about the IP IO addresses if it's marked
>>>>> with status = "disabled".. Which IP are you having problems with?
>>>>>
>>>>>> which is why I needed the ti,no-init for the epos evm. It isn't just a
>>>>>> matter of we shouldnt write to it because we don't want to use it; we
>>>>>> can't write to it because the module is held off so it causes an
>>>>>> external abort if we do.
>>>>>
>>>>> Well hard to say not knowing which module this is.. Pretty much all
>>>>> the modules have drivers and the driver just does pm_runtime_get()
>>>>> on it?
>>>>
>>>> Heh OK this thread is about the RTC driver, so I assume that's the
>>>> problem :) So if you set the rtc to status = "disabled" how can the
>>>> hwmod code do anything as AFAIK it won't even get the rtc IO address?
>>>>
>>>> Or am I missing something here?
>>>
>>> Perhaps I am mistaken, but from what I understand, all hwmods have _init and
>>> _setup called on them, and all hwmods read the IO address regardless of DT
>>> status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
>>> which calls _enable for the hwmod, and this calls both _enable_sysc and
>>> _update_sysc_cache which touch the sysconfig register of the IP.
>>
>> Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(),
>> sorry. Looks like the hwmod IO address data does get populated even
>> for status = "disabled" although the dev entry won't get created and
>> omap_device_build_from_dt() never gets called.
>>
>>> Normally this is fine regardless of whether or not we are using an IP because
>>> the module will wake up for a moment, have it's sysc programmed, and then be put
>>> back to sleep later, potentially never to be woken again if we bind no driver
>>> for it, which is fine for 99% of cases. In the case of am43x epos evm, you can
>>> take the same piece of silicon that will boot happily on the gp evm with the rtc
>>> hwmod in place and it will hang during boot on the epos evm because the board
>>> uses a pin to hold the RTC IP in reset. There is no way to detect this in
>>> software, the module can be turned on as normal using the clk_ctrl, but if you
>>> touch any of the IP registers you get an abort.
>>
>> OK sounds like some dts property is needed to signal this.
> 
> As I understand, there is device "RTC" and this device has status 'disabled',
> so there is reasonable question why do we need to touch it at all?
> The HWMOD is some kind of SoC description, which was needed before DT.
> Now with DT in place it seems unreasonable to touch any IP block which:
> - are not defined in DT
> - has status 'disabled'.
> in above cases the u-boot has to dial with IP block if it's invisible for Kernel.
> 
> The HWMOD framework intended to reset and put in some predefined states IPs which are
> visible for the Kernel, so then proper driver can start working with IP or IP will be
> kept in some low-power state if there is no driver.

Currently we still need this hwmod behavior as not all IPs are in an ideal state
for PM by default. Not sure if you saw my last email in this thread but I gave
an example for USB hwmod:

If no USB driver is bound even just letting omap_device idle it using the USB_
CLKCTRL in the PRCM will not work properly, because the USB on am33xx expects
it's SYSCONFIG STANDBY_MODE to be software supervised, the default state
(SMART_STANDBY) does not let the IP go into standby so the IP gets stuck in a
partially off state but does not actually shut down as expected.

So we need to be able to touch the dt nodes even if they are marked as disabled
because we need to get the IO address to have access to the SYSCONFIG register.
I am not trying to introduce any major new changes to omap_hwmod layer, I am
just trying to allow it to work in more situations.

This flag would only exist to PREVENT any hwmod action from happening in certain
cases where we cannot even touch the IP for whatever reason (in the first case
that this patch intends to be used for, the RTC IP on am43x-epos-evm which is
disabled by the board configuration).

Regards,
Dave

> 
> Such kind of changes really confused :(, because when I'm looking on DT and see - status='disabled'
> I suppose that such IP will not be touched by Kernel. But it's NOT really 'disabled'.
> It's kinda 'partially disabled' or 'not present' or 'unused' ..
> (if someone will decide to continue with such approach - it could be more
> useful to define new value for 'status' parameter :P).
> Also, just imaging that OMAP kernel is used with Xen as DomU and how hard will
> it be to find and cut off all such tricks :( 
> 
> Did I miss something?
>
>>   
>>> So we need to prevent this from happening but of course we can't selectively
>>> choose when the rtc hwmod gets added based on which board we are using so it
>>> seemed a DT flag was appropriate to indicate that we do not want to init the rtc
>>> IP at all only on this board.
>>>
>>> Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
>>> fails booting with an imprecise abort.
>>
>> OK thanks for explaining it. I'm fine with this patch, Paul may have
>> other issues. The other option would be to use status = "disabled" to
>> not touch the device at all like Paul suggested. I wonder if that's
>> going to break PM on some devices though..
>>
> 
> Regards,
> -grygorii
> 

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Grygorii Strashko March 11, 2015, 4:32 p.m. UTC | #11
Hi Dave,

On 03/10/2015 07:59 PM, Dave Gerlach wrote:
> On 03/10/2015 12:36 PM, Grygorii Strashko wrote:
>> On 03/06/2015 07:45 PM, Tony Lindgren wrote:
>>> * Dave Gerlach <d-gerlach@ti.com> [150306 09:28]:
>>>> On 03/05/2015 06:41 PM, Tony Lindgren wrote:
>>>>> * Tony Lindgren <tony@atomide.com> [150305 12:24]:
>>>>>> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
>>>>>>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
>>>>>>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>>>>>>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>>>>>>>>
>>>>>>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>>>>>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>>>>>>>>> the hwmod and programs the sysconfig before attempting to idle it at
>>>>>>>>>> boot. If an IP has been disabled by the hardware configuration on a
>>>>>>>>>> platform, this will cause a hang due to writing to inactive registers.
>>>>>>>>>> This property prevents that from happening by marking the hwmod as
>>>>>>>>>> _HWMOD_STATE_DISABLED during init.
>>>>>>>>>
>>>>>>>>> I'm kind of wondering if hwmod should even touch a device if it's marked
>>>>>>>>> as disabled in the DT.  Tony, what do you think?
>>>>>>>>
>>>>>>>> Well nothing happens if a device is status = "disabled". No dev entry
>>>>>>>> gets created for it at all and hwmod won't have any data for the device
>>>>>>>> populated. The only way hwmod code could see that device if the device
>>>>>>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
>>>>>>>>
>>>>>>>
>>>>>>> We still need this for the sysconfig programming, correct? hwmod programs that
>>>>>>> regardless of dt status and then idles the IP,
>>>>>>
>>>>>> Well hwmod does not even know about the IP IO addresses if it's marked
>>>>>> with status = "disabled".. Which IP are you having problems with?
>>>>>>
>>>>>>> which is why I needed the ti,no-init for the epos evm. It isn't just a
>>>>>>> matter of we shouldnt write to it because we don't want to use it; we
>>>>>>> can't write to it because the module is held off so it causes an
>>>>>>> external abort if we do.
>>>>>>
>>>>>> Well hard to say not knowing which module this is.. Pretty much all
>>>>>> the modules have drivers and the driver just does pm_runtime_get()
>>>>>> on it?
>>>>>
>>>>> Heh OK this thread is about the RTC driver, so I assume that's the
>>>>> problem :) So if you set the rtc to status = "disabled" how can the
>>>>> hwmod code do anything as AFAIK it won't even get the rtc IO address?
>>>>>
>>>>> Or am I missing something here?
>>>>
>>>> Perhaps I am mistaken, but from what I understand, all hwmods have _init and
>>>> _setup called on them, and all hwmods read the IO address regardless of DT
>>>> status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
>>>> which calls _enable for the hwmod, and this calls both _enable_sysc and
>>>> _update_sysc_cache which touch the sysconfig register of the IP.

And that's the problem :) What ePar says:
“disabled” - Indicates that the device is not presently operational, but it might
become operational in the future (for example, something is not plugged in, or switched off).

and current OF implementation will not register corresponding device
in DD core and, as result, drivers will be never ever bound with these devices.
As i said before, such devices are invisible/absent/not present, so
there are no reasons to touch them at all in Kernel, because result is unpredictable
in general. And there are no guarantee that there will be no other issues, 
even if you'll fix this particular case. 

>>>
>>> Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(),
>>> sorry. Looks like the hwmod IO address data does get populated even
>>> for status = "disabled" although the dev entry won't get created and
>>> omap_device_build_from_dt() never gets called.
>>>
>>>> Normally this is fine regardless of whether or not we are using an IP because
>>>> the module will wake up for a moment, have it's sysc programmed, and then be put
>>>> back to sleep later, potentially never to be woken again if we bind no driver
>>>> for it, which is fine for 99% of cases. In the case of am43x epos evm, you can

^^ if status=“disabled”/"failed" there will be no device and no driver will have been bound :)

>>>> take the same piece of silicon that will boot happily on the gp evm with the rtc
>>>> hwmod in place and it will hang during boot on the epos evm because the board
>>>> uses a pin to hold the RTC IP in reset. There is no way to detect this in
>>>> software, the module can be turned on as normal using the clk_ctrl, but if you
>>>> touch any of the IP registers you get an abort.
>>>
>>> OK sounds like some dts property is needed to signal this.

Seems It might be much more simple to just remove RTC device from DT, as 
it's disabled and unaccessible == not present:
- add am4372-rtc.dtsi and put RTC device definition there
- include am4372-rtc.dtsi in board files where allowed


>>
>> As I understand, there is device "RTC" and this device has status 'disabled',
>> so there is reasonable question why do we need to touch it at all?
>> The HWMOD is some kind of SoC description, which was needed before DT.
>> Now with DT in place it seems unreasonable to touch any IP block which:
>> - are not defined in DT
>> - has status 'disabled'.
>> in above cases the u-boot has to dial with IP block if it's invisible for Kernel.
>>
>> The HWMOD framework intended to reset and put in some predefined states IPs which are
>> visible for the Kernel, so then proper driver can start working with IP or IP will be
>> kept in some low-power state if there is no driver.
> 
> Currently we still need this hwmod behavior as not all IPs are in an ideal state
> for PM by default. Not sure if you saw my last email in this thread but I gave
> an example for USB hwmod:
> 
> If no USB driver is bound even just letting omap_device idle it using the USB_
> CLKCTRL in the PRCM will not work properly, because the USB on am33xx expects
> it's SYSCONFIG STANDBY_MODE to be software supervised, the default state
> (SMART_STANDBY) does not let the IP go into standby so the IP gets stuck in a
> partially off state but does not actually shut down as expected.
> 
> So we need to be able to touch the dt nodes even if they are marked as disabled
> because we need to get the IO address to have access to the SYSCONFIG register.
> I am not trying to introduce any major new changes to omap_hwmod layer, I am
> just trying to allow it to work in more situations.


Oh yes! And this happen just due to historical reasons ;) 
The HWMOD is ancient thing :P which was created at time when:
- all OMAP's code was built-in
- there were no DT in place.
And it actually was created to describe configuration and integration of HW.
But now there is DT which is intended for the same purposes and HWMOD data is
still here (as i know) just because process of migration to DT is not fully completed yet.
More over, now we have multiplatform; restriction to put SoC's erratas and hacks in kernel;
and all drivers going to be converted to loadable modules.

In my opinion, this is not good when we have device marked as 'disabled',
but Kernel still tries to access them. More over, we need to completely remove device's
definitions from DT to prevent Kernel of touching such devices.

So, let's not make things worse than they are :( and just remove RTC device where it's not needed.

> 
> This flag would only exist to PREVENT any hwmod action from happening in certain
> cases where we cannot even touch the IP for whatever reason (in the first case
> that this patch intends to be used for, the RTC IP on am43x-epos-evm which is
> disabled by the board configuration).
> 
>>
>> Such kind of changes really confused :(, because when I'm looking on DT and see - status='disabled'
>> I suppose that such IP will not be touched by Kernel. But it's NOT really 'disabled'.
>> It's kinda 'partially disabled' or 'not present' or 'unused' ..
>> (if someone will decide to continue with such approach - it could be more
>> useful to define new value for 'status' parameter :P).
>> Also, just imaging that OMAP kernel is used with Xen as DomU and how hard will
>> it be to find and cut off all such tricks :(
>>
>> Did I miss something?
>>
>>>    
>>>> So we need to prevent this from happening but of course we can't selectively
>>>> choose when the rtc hwmod gets added based on which board we are using so it
>>>> seemed a DT flag was appropriate to indicate that we do not want to init the rtc
>>>> IP at all only on this board.
>>>>
>>>> Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
>>>> fails booting with an imprecise abort.
>>>
>>> OK thanks for explaining it. I'm fine with this patch, Paul may have
>>> other issues. The other option would be to use status = "disabled" to
>>> not touch the device at all like Paul suggested. I wonder if that's
>>> going to break PM on some devices though..

That how it should be as for me, but unfortunately, it could break PM :(, 
because It's common assumption now that Kernel will
reset & disable ALL OMAP's devices regardless of DT. 

It could be possible if it will be handled properly outside of
the kernel - in u-boot for example.

regards,
-grygorii
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Dave Gerlach March 12, 2015, 8:05 p.m. UTC | #12
Grygorii,
On 03/11/2015 11:32 AM, Grygorii Strashko wrote:
> Hi Dave,
> 
> On 03/10/2015 07:59 PM, Dave Gerlach wrote:
>> On 03/10/2015 12:36 PM, Grygorii Strashko wrote:
>>> On 03/06/2015 07:45 PM, Tony Lindgren wrote:
>>>> * Dave Gerlach <d-gerlach@ti.com> [150306 09:28]:
>>>>> On 03/05/2015 06:41 PM, Tony Lindgren wrote:
>>>>>> * Tony Lindgren <tony@atomide.com> [150305 12:24]:
>>>>>>> * Dave Gerlach <d-gerlach@ti.com> [150305 11:53]:
>>>>>>>> On 03/05/2015 12:49 PM, Tony Lindgren wrote:
>>>>>>>>> * Paul Walmsley <paul@pwsan.com> [150305 10:16]:
>>>>>>>>>> On Thu, 5 Mar 2015, Dave Gerlach wrote:
>>>>>>>>>>
>>>>>>>>>>> Introduce a dt property, ti,no-init, that prevents hwmod initialization.
>>>>>>>>>>> Even if a dt node is marked as disabled, hwmod still at least enables
>>>>>>>>>>> the hwmod and programs the sysconfig before attempting to idle it at
>>>>>>>>>>> boot. If an IP has been disabled by the hardware configuration on a
>>>>>>>>>>> platform, this will cause a hang due to writing to inactive registers.
>>>>>>>>>>> This property prevents that from happening by marking the hwmod as
>>>>>>>>>>> _HWMOD_STATE_DISABLED during init.
>>>>>>>>>>
>>>>>>>>>> I'm kind of wondering if hwmod should even touch a device if it's marked
>>>>>>>>>> as disabled in the DT.  Tony, what do you think?
>>>>>>>>>
>>>>>>>>> Well nothing happens if a device is status = "disabled". No dev entry
>>>>>>>>> gets created for it at all and hwmod won't have any data for the device
>>>>>>>>> populated. The only way hwmod code could see that device if the device
>>>>>>>>> gets it's data from the legacy omap_hwmod_*_data.c instead of DT.
>>>>>>>>>
>>>>>>>>
>>>>>>>> We still need this for the sysconfig programming, correct? hwmod programs that
>>>>>>>> regardless of dt status and then idles the IP,
>>>>>>>
>>>>>>> Well hwmod does not even know about the IP IO addresses if it's marked
>>>>>>> with status = "disabled".. Which IP are you having problems with?
>>>>>>>
>>>>>>>> which is why I needed the ti,no-init for the epos evm. It isn't just a
>>>>>>>> matter of we shouldnt write to it because we don't want to use it; we
>>>>>>>> can't write to it because the module is held off so it causes an
>>>>>>>> external abort if we do.
>>>>>>>
>>>>>>> Well hard to say not knowing which module this is.. Pretty much all
>>>>>>> the modules have drivers and the driver just does pm_runtime_get()
>>>>>>> on it?
>>>>>>
>>>>>> Heh OK this thread is about the RTC driver, so I assume that's the
>>>>>> problem :) So if you set the rtc to status = "disabled" how can the
>>>>>> hwmod code do anything as AFAIK it won't even get the rtc IO address?
>>>>>>
>>>>>> Or am I missing something here?
>>>>>
>>>>> Perhaps I am mistaken, but from what I understand, all hwmods have _init and
>>>>> _setup called on them, and all hwmods read the IO address regardless of DT
>>>>> status at this point with _init_mpu_rt_base. In _setup, _setup_reset gets called
>>>>> which calls _enable for the hwmod, and this calls both _enable_sysc and
>>>>> _update_sysc_cache which touch the sysconfig register of the IP.
> 
> And that's the problem :) What ePar says:
> “disabled” - Indicates that the device is not presently operational, but it might
> become operational in the future (for example, something is not plugged in, or switched off).
> 
> and current OF implementation will not register corresponding device
> in DD core and, as result, drivers will be never ever bound with these devices.
> As i said before, such devices are invisible/absent/not present, so
> there are no reasons to touch them at all in Kernel, because result is unpredictable
> in general. And there are no guarantee that there will be no other issues, 
> even if you'll fix this particular case.

I agree with all of this, but we can't do this entirely without breaking PM, at
least until omap_hwmod is entirely gone. If we were to prevent omap_hwmod from
touching any dt node marked as disabled, then we aren't going to be able to idle
all IPs. omap_hwmod/omap_device handles idling of unused IPs, and we many times
need the SYSCONFIG register to do that, so we can't ignore ALL disabled dt nodes
until that system is replaced. I dont think it's reasonable to ask people to
include every single driver just to get PM. But, this is far beyond the scope of
what this patch is trying to solve.

> 
>>>>
>>>> Oh OK, I think you're right. I was thinking of omap_device_build_from_dt(),
>>>> sorry. Looks like the hwmod IO address data does get populated even
>>>> for status = "disabled" although the dev entry won't get created and
>>>> omap_device_build_from_dt() never gets called.
>>>>
>>>>> Normally this is fine regardless of whether or not we are using an IP because
>>>>> the module will wake up for a moment, have it's sysc programmed, and then be put
>>>>> back to sleep later, potentially never to be woken again if we bind no driver
>>>>> for it, which is fine for 99% of cases. In the case of am43x epos evm, you can
> 
> ^^ if status=“disabled”/"failed" there will be no device and no driver will have been bound :)
> 
>>>>> take the same piece of silicon that will boot happily on the gp evm with the rtc
>>>>> hwmod in place and it will hang during boot on the epos evm because the board
>>>>> uses a pin to hold the RTC IP in reset. There is no way to detect this in
>>>>> software, the module can be turned on as normal using the clk_ctrl, but if you
>>>>> touch any of the IP registers you get an abort.
>>>>
>>>> OK sounds like some dts property is needed to signal this.
> 
> Seems It might be much more simple to just remove RTC device from DT, as 
> it's disabled and unaccessible == not present:
> - add am4372-rtc.dtsi and put RTC device definition there
> - include am4372-rtc.dtsi in board files where allowed

Well this would work, but only because you trick omap_hwmod by not providing an
IO address for the RTC in the case of am43x-epos-evm, so we would still get a
boot warning about not having an address for the RTC hwmod, but if this is
acceptable, it would work, not break boot, and require no changes to the
omap_hwmod core.

> 
> 
>>>
>>> As I understand, there is device "RTC" and this device has status 'disabled',
>>> so there is reasonable question why do we need to touch it at all?
>>> The HWMOD is some kind of SoC description, which was needed before DT.
>>> Now with DT in place it seems unreasonable to touch any IP block which:
>>> - are not defined in DT
>>> - has status 'disabled'.
>>> in above cases the u-boot has to dial with IP block if it's invisible for Kernel.
>>>
>>> The HWMOD framework intended to reset and put in some predefined states IPs which are
>>> visible for the Kernel, so then proper driver can start working with IP or IP will be
>>> kept in some low-power state if there is no driver.
>>
>> Currently we still need this hwmod behavior as not all IPs are in an ideal state
>> for PM by default. Not sure if you saw my last email in this thread but I gave
>> an example for USB hwmod:
>>
>> If no USB driver is bound even just letting omap_device idle it using the USB_
>> CLKCTRL in the PRCM will not work properly, because the USB on am33xx expects
>> it's SYSCONFIG STANDBY_MODE to be software supervised, the default state
>> (SMART_STANDBY) does not let the IP go into standby so the IP gets stuck in a
>> partially off state but does not actually shut down as expected.
>>
>> So we need to be able to touch the dt nodes even if they are marked as disabled
>> because we need to get the IO address to have access to the SYSCONFIG register.
>> I am not trying to introduce any major new changes to omap_hwmod layer, I am
>> just trying to allow it to work in more situations.
> 
> 
> Oh yes! And this happen just due to historical reasons ;) 
> The HWMOD is ancient thing :P which was created at time when:
> - all OMAP's code was built-in
> - there were no DT in place.
> And it actually was created to describe configuration and integration of HW.
> But now there is DT which is intended for the same purposes and HWMOD data is
> still here (as i know) just because process of migration to DT is not fully completed yet.
> More over, now we have multiplatform; restriction to put SoC's erratas and hacks in kernel;
> and all drivers going to be converted to loadable modules.
> 
> In my opinion, this is not good when we have device marked as 'disabled',
> but Kernel still tries to access them. More over, we need to completely remove device's
> definitions from DT to prevent Kernel of touching such devices.
> 
> So, let's not make things worse than they are :( and just remove RTC device where it's not needed.

As I said above this would work but I do not know if it's more correct to trick
omap_hwmod with the DT or change omap_hwmod with ti,no-init, because we are
still using it today.

Regards,
Dave

> 
>>
>> This flag would only exist to PREVENT any hwmod action from happening in certain
>> cases where we cannot even touch the IP for whatever reason (in the first case
>> that this patch intends to be used for, the RTC IP on am43x-epos-evm which is
>> disabled by the board configuration).
>>
>>>
>>> Such kind of changes really confused :(, because when I'm looking on DT and see - status='disabled'
>>> I suppose that such IP will not be touched by Kernel. But it's NOT really 'disabled'.
>>> It's kinda 'partially disabled' or 'not present' or 'unused' ..
>>> (if someone will decide to continue with such approach - it could be more
>>> useful to define new value for 'status' parameter :P).
>>> Also, just imaging that OMAP kernel is used with Xen as DomU and how hard will
>>> it be to find and cut off all such tricks :(
>>>
>>> Did I miss something?
>>>
>>>>    
>>>>> So we need to prevent this from happening but of course we can't selectively
>>>>> choose when the rtc hwmod gets added based on which board we are using so it
>>>>> seemed a DT flag was appropriate to indicate that we do not want to init the rtc
>>>>> IP at all only on this board.
>>>>>
>>>>> Without this flag in place but with the rtc hwmod added, the am43x-epos-evm
>>>>> fails booting with an imprecise abort.
>>>>
>>>> OK thanks for explaining it. I'm fine with this patch, Paul may have
>>>> other issues. The other option would be to use status = "disabled" to
>>>> not touch the device at all like Paul suggested. I wonder if that's
>>>> going to break PM on some devices though..
> 
> That how it should be as for me, but unfortunately, it could break PM :(, 
> because It's common assumption now that Kernel will
> reset & disable ALL OMAP's devices regardless of DT. 
> 
> It could be possible if it will be handled properly outside of
> the kernel - in u-boot for example.
> 
> regards,
> -grygorii
> 

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diff mbox

Patch

diff --git a/Documentation/devicetree/bindings/arm/omap/omap.txt b/Documentation/devicetree/bindings/arm/omap/omap.txt
index 4f6a82c..7c0d3a53 100644
--- a/Documentation/devicetree/bindings/arm/omap/omap.txt
+++ b/Documentation/devicetree/bindings/arm/omap/omap.txt
@@ -23,6 +23,8 @@  Optional properties:
   during suspend.
 - ti,no-reset-on-init: When present, the module should not be reset at init
 - ti,no-idle-on-init: When present, the module should not be idled at init
+- ti,no_init: When present, the module is marked as disabled immediately and
+  no setup is done.
 
 Example:
 
diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c
index 92afb72..e835f61 100644
--- a/arch/arm/mach-omap2/omap_hwmod.c
+++ b/arch/arm/mach-omap2/omap_hwmod.c
@@ -2471,9 +2471,14 @@  static int __init _init(struct omap_hwmod *oh, void *data)
 			oh->flags |= HWMOD_INIT_NO_RESET;
 		if (of_find_property(np, "ti,no-idle-on-init", NULL))
 			oh->flags |= HWMOD_INIT_NO_IDLE;
+		if (of_find_property(np, "ti,no-init", NULL))
+			oh->flags |= HWMOD_NO_INIT;
 	}
 
-	oh->_state = _HWMOD_STATE_INITIALIZED;
+	if (oh->flags & HWMOD_NO_INIT)
+		oh->_state = _HWMOD_STATE_DISABLED;
+	else
+		oh->_state = _HWMOD_STATE_INITIALIZED;
 
 	return 0;
 }
diff --git a/arch/arm/mach-omap2/omap_hwmod.h b/arch/arm/mach-omap2/omap_hwmod.h
index 9d4bec6e..75061fc 100644
--- a/arch/arm/mach-omap2/omap_hwmod.h
+++ b/arch/arm/mach-omap2/omap_hwmod.h
@@ -517,6 +517,9 @@  struct omap_hwmod_omap4_prcm {
  * HWMOD_RECONFIG_IO_CHAIN: omap_hwmod code needs to reconfigure wake-up 
  *     events by calling _reconfigure_io_chain() when a device is enabled
  *     or idled.
+ * HWMOD_NO_INIT: Do not initialize the hwmod. Useful for when certain
+ *     platforms disable the IP through hardware configuration, like the
+ *     RTC on the AM437x EPOS EVM.
  */
 #define HWMOD_SWSUP_SIDLE			(1 << 0)
 #define HWMOD_SWSUP_MSTANDBY			(1 << 1)
@@ -532,6 +535,7 @@  struct omap_hwmod_omap4_prcm {
 #define HWMOD_FORCE_MSTANDBY			(1 << 11)
 #define HWMOD_SWSUP_SIDLE_ACT			(1 << 12)
 #define HWMOD_RECONFIG_IO_CHAIN			(1 << 13)
+#define HWMOD_NO_INIT				(1 << 14)
 
 /*
  * omap_hwmod._int_flags definitions