diff mbox series

[RFC,1/4] dt-binding: i2c: add generic properties for GPIO bus recovery

Message ID 20200619141904.910889-2-codrin.ciubotariu@microchip.com
State Superseded
Headers show
Series i2c: core: add generic GPIO bus recovery | expand

Commit Message

Codrin Ciubotariu June 19, 2020, 2:19 p.m. UTC
The I2C GPIO bus recovery properties consist of two GPIOS and one extra
pinctrl state ("gpio" or "recovery"). Not all are mandatory for recovery.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
---
 Documentation/devicetree/bindings/i2c/i2c.txt | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Wolfram Sang July 5, 2020, 9:19 p.m. UTC | #1
> +- pinctrl
> +	add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
> +	recovery, call it "gpio" or "recovery" state

I think we should stick with "gpio" only. That is what at91 and imx have
in their bindings. pxa uses "recovery" as a pinctrl state name but I
can't find any further use or documentation of that. PXA is not fully
converted to the best of my knowledge, so maybe it is no problem for PXA
to switch to "gpio", too? We should ask Russell King (cced).

Russell, do you object naming the pinctrl state for bus recovery in
the pxa i2c driver from "recovery" to "gpio"?
Rob Herring July 15, 2020, 7:21 p.m. UTC | #2
On Fri, 19 Jun 2020 17:19:01 +0300, Codrin Ciubotariu wrote:
> The I2C GPIO bus recovery properties consist of two GPIOS and one extra
> pinctrl state ("gpio" or "recovery"). Not all are mandatory for recovery.
> 
> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
> ---
>  Documentation/devicetree/bindings/i2c/i2c.txt | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 

Reviewed-by: Rob Herring <robh@kernel.org>
Wolfram Sang July 24, 2020, 7:39 p.m. UTC | #3
On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
> 
> > +- pinctrl
> > +	add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
> > +	recovery, call it "gpio" or "recovery" state
> 
> I think we should stick with "gpio" only. That is what at91 and imx have
> in their bindings. pxa uses "recovery" as a pinctrl state name but I
> can't find any further use or documentation of that. PXA is not fully
> converted to the best of my knowledge, so maybe it is no problem for PXA
> to switch to "gpio", too? We should ask Russell King (cced).
> 
> Russell, do you object naming the pinctrl state for bus recovery in
> the pxa i2c driver from "recovery" to "gpio"?

No response, so far. I suggest now to support the "recovery" naming but
mark it as deprecated. Opinions?
Russell King - ARM Linux admin July 24, 2020, 8:52 p.m. UTC | #4
On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
> > 
> > > +- pinctrl
> > > +	add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
> > > +	recovery, call it "gpio" or "recovery" state
> > 
> > I think we should stick with "gpio" only. That is what at91 and imx have
> > in their bindings. pxa uses "recovery" as a pinctrl state name but I
> > can't find any further use or documentation of that. PXA is not fully
> > converted to the best of my knowledge, so maybe it is no problem for PXA
> > to switch to "gpio", too? We should ask Russell King (cced).

Fully converted to what?  The generic handling where the i2c core layer
handles everything to do with recovery, including the switch between
modes?

i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
GPIO mode, and I don't see a generic driver doing that to avoid causing
any additional glitches on the bus.  Given the use case that this recovery
is targetted at, avoiding glitches is very important to keep.

> > Russell, do you object naming the pinctrl state for bus recovery in
> > the pxa i2c driver from "recovery" to "gpio"?
> 
> No response, so far. I suggest now to support the "recovery" naming but
> mark it as deprecated. Opinions?

I don't have a preference on the exact naming.
Codrin Ciubotariu July 27, 2020, 10:44 a.m. UTC | #5
On 24.07.2020 23:52, Russell King - ARM Linux admin wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
>>>
>>>> +- pinctrl
>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
>>>> + recovery, call it "gpio" or "recovery" state
>>>
>>> I think we should stick with "gpio" only. That is what at91 and imx have
>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I
>>> can't find any further use or documentation of that. PXA is not fully
>>> converted to the best of my knowledge, so maybe it is no problem for PXA
>>> to switch to "gpio", too? We should ask Russell King (cced).
> 
> Fully converted to what?  The generic handling where the i2c core layer
> handles everything to do with recovery, including the switch between
> modes?
> 
> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
> GPIO mode, and I don't see a generic driver doing that to avoid causing
> any additional glitches on the bus.  Given the use case that this recovery
> is targetted at, avoiding glitches is very important to keep.

Why is it not possbile to handle glitches in a generic way? I guess it 
depends on the pinctl, but we could treat a worst-case scenario to 
assure the switch between states is done properly.

> 
>>> Russell, do you object naming the pinctrl state for bus recovery in
>>> the pxa i2c driver from "recovery" to "gpio"?
>>
>> No response, so far. I suggest now to support the "recovery" naming but
>> mark it as deprecated. Opinions?
> 
> I don't have a preference on the exact naming.
> 
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
>
Russell King - ARM Linux admin July 27, 2020, 10:50 a.m. UTC | #6
On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote:
> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
> >> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
> >>>
> >>>> +- pinctrl
> >>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
> >>>> + recovery, call it "gpio" or "recovery" state
> >>>
> >>> I think we should stick with "gpio" only. That is what at91 and imx have
> >>> in their bindings. pxa uses "recovery" as a pinctrl state name but I
> >>> can't find any further use or documentation of that. PXA is not fully
> >>> converted to the best of my knowledge, so maybe it is no problem for PXA
> >>> to switch to "gpio", too? We should ask Russell King (cced).
> > 
> > Fully converted to what?  The generic handling where the i2c core layer
> > handles everything to do with recovery, including the switch between
> > modes?
> > 
> > i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
> > GPIO mode, and I don't see a generic driver doing that to avoid causing
> > any additional glitches on the bus.  Given the use case that this recovery
> > is targetted at, avoiding glitches is very important to keep.
> 
> Why is it not possbile to handle glitches in a generic way? I guess it 
> depends on the pinctl, but we could treat a worst-case scenario to 
> assure the switch between states is done properly.

Please look at how i2c-pxa switches between the two, and decide whether
the generic implementation can do the same.
Codrin Ciubotariu July 30, 2020, 9 a.m. UTC | #7
On 27.07.2020 13:50, Russell King - ARM Linux admin wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote:
>> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
>>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
>>>>>
>>>>>> +- pinctrl
>>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
>>>>>> + recovery, call it "gpio" or "recovery" state
>>>>>
>>>>> I think we should stick with "gpio" only. That is what at91 and imx have
>>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I
>>>>> can't find any further use or documentation of that. PXA is not fully
>>>>> converted to the best of my knowledge, so maybe it is no problem for PXA
>>>>> to switch to "gpio", too? We should ask Russell King (cced).
>>>
>>> Fully converted to what?  The generic handling where the i2c core layer
>>> handles everything to do with recovery, including the switch between
>>> modes?
>>>
>>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
>>> GPIO mode, and I don't see a generic driver doing that to avoid causing
>>> any additional glitches on the bus.  Given the use case that this recovery
>>> is targetted at, avoiding glitches is very important to keep.
>>
>> Why is it not possbile to handle glitches in a generic way? I guess it
>> depends on the pinctl, but we could treat a worst-case scenario to
>> assure the switch between states is done properly.
> 
> Please look at how i2c-pxa switches between the two, and decide whether
> the generic implementation can do the same.

The handling of glitches from initialization looks generic to me. I see 
that there are specific clear/reset routines that are in the 
(un)prepare_recovery() callbacks, but these callbacks are not replaced 
by the generic i2c recovery and will still be used if given by the 
driver. The only thing the generic recovery does is to switch the pinmux 
state. We can discuss whether we want to change the pinmux state first 
or call the (un)preapre_recovery().
What I had in mind for the generic recovery was to just handle the 
common parts that follow the same bindings, which is getting the gpios 
and changing the pinmux states before recovering.

Best regards,
Codrin

> 
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
>
Russell King - ARM Linux admin Aug. 3, 2020, 2:16 p.m. UTC | #8
On Thu, Jul 30, 2020 at 09:00:36AM +0000, Codrin.Ciubotariu@microchip.com wrote:
> On 27.07.2020 13:50, Russell King - ARM Linux admin wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote:
> >> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote:
> >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>>
> >>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
> >>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
> >>>>>
> >>>>>> +- pinctrl
> >>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
> >>>>>> + recovery, call it "gpio" or "recovery" state
> >>>>>
> >>>>> I think we should stick with "gpio" only. That is what at91 and imx have
> >>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I
> >>>>> can't find any further use or documentation of that. PXA is not fully
> >>>>> converted to the best of my knowledge, so maybe it is no problem for PXA
> >>>>> to switch to "gpio", too? We should ask Russell King (cced).
> >>>
> >>> Fully converted to what?  The generic handling where the i2c core layer
> >>> handles everything to do with recovery, including the switch between
> >>> modes?
> >>>
> >>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
> >>> GPIO mode, and I don't see a generic driver doing that to avoid causing
> >>> any additional glitches on the bus.  Given the use case that this recovery
> >>> is targetted at, avoiding glitches is very important to keep.
> >>
> >> Why is it not possbile to handle glitches in a generic way? I guess it
> >> depends on the pinctl, but we could treat a worst-case scenario to
> >> assure the switch between states is done properly.
> > 
> > Please look at how i2c-pxa switches between the two, and decide whether
> > the generic implementation can do the same.
> 
> The handling of glitches from initialization looks generic to me. I see 
> that there are specific clear/reset routines that are in the 
> (un)prepare_recovery() callbacks, but these callbacks are not replaced 
> by the generic i2c recovery and will still be used if given by the 
> driver. The only thing the generic recovery does is to switch the pinmux 
> state. We can discuss whether we want to change the pinmux state first 
> or call the (un)preapre_recovery().

Right, the key point i2c-pxa does is that on prepare:
- read the current state of the SCL and SDA lines and set the GPIO to
  reflect those values.
- then switch the pinmux state.

That must be preserved, otherwise if SCL is being held low by the I2C
master, and we switch to GPIO mode, SCL will be released.  So the
driver needs to be involved before the pinmux state is changed.
Codrin Ciubotariu Aug. 3, 2020, 4:42 p.m. UTC | #9
On 03.08.2020 17:16, Russell King - ARM Linux admin wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Thu, Jul 30, 2020 at 09:00:36AM +0000, Codrin.Ciubotariu@microchip.com wrote:
>> On 27.07.2020 13:50, Russell King - ARM Linux admin wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote:
>>>> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote:
>>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>>
>>>>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
>>>>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
>>>>>>>
>>>>>>>> +- pinctrl
>>>>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
>>>>>>>> + recovery, call it "gpio" or "recovery" state
>>>>>>>
>>>>>>> I think we should stick with "gpio" only. That is what at91 and imx have
>>>>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I
>>>>>>> can't find any further use or documentation of that. PXA is not fully
>>>>>>> converted to the best of my knowledge, so maybe it is no problem for PXA
>>>>>>> to switch to "gpio", too? We should ask Russell King (cced).
>>>>>
>>>>> Fully converted to what?  The generic handling where the i2c core layer
>>>>> handles everything to do with recovery, including the switch between
>>>>> modes?
>>>>>
>>>>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
>>>>> GPIO mode, and I don't see a generic driver doing that to avoid causing
>>>>> any additional glitches on the bus.  Given the use case that this recovery
>>>>> is targetted at, avoiding glitches is very important to keep.
>>>>
>>>> Why is it not possbile to handle glitches in a generic way? I guess it
>>>> depends on the pinctl, but we could treat a worst-case scenario to
>>>> assure the switch between states is done properly.
>>>
>>> Please look at how i2c-pxa switches between the two, and decide whether
>>> the generic implementation can do the same.
>>
>> The handling of glitches from initialization looks generic to me. I see
>> that there are specific clear/reset routines that are in the
>> (un)prepare_recovery() callbacks, but these callbacks are not replaced
>> by the generic i2c recovery and will still be used if given by the
>> driver. The only thing the generic recovery does is to switch the pinmux
>> state. We can discuss whether we want to change the pinmux state first
>> or call the (un)preapre_recovery().
> 
> Right, the key point i2c-pxa does is that on prepare:
> - read the current state of the SCL and SDA lines and set the GPIO to
>    reflect those values.
> - then switch the pinmux state.
> 
> That must be preserved, otherwise if SCL is being held low by the I2C
> master, and we switch to GPIO mode, SCL will be released.  So the
> driver needs to be involved before the pinmux state is changed.

I understand, and I admit that I didn't see this case. In my mind, the 
master would always be in (almost) a reset state before calling for SDA 
recovery, so it won't hold any lines.
These steps can't be generic, of course. Also, not all I2C masters have 
a way to show the state of its lines. For these masters, one idea would 
be to reset them before calling i2c_recover_bus()

> 
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
>
diff mbox series

Patch

diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
index 438ae123107e..6a644a24fc1c 100644
--- a/Documentation/devicetree/bindings/i2c/i2c.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c.txt
@@ -77,6 +77,16 @@  wants to support one of the below features, it should adapt these bindings.
 	this information to detect a stalled bus more reliably, for example.
 	Can not be combined with 'multi-master'.
 
+- scl-gpios
+	specify the gpio related to SCL pin. Used for GPIO bus recovery.
+
+- sda-gpios
+	specify the gpio related to SDA pin. Optional for GPIO bus recovery.
+
+- pinctrl
+	add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
+	recovery, call it "gpio" or "recovery" state
+
 Required properties (per child device)
 --------------------------------------