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[v2,0/2] Sluggish AT91 I2C driver causes SMBus timeouts

Message ID 20171127163101.27859-1-peda@axentia.se
Headers show
Series Sluggish AT91 I2C driver causes SMBus timeouts | expand

Message

Peter Rosin Nov. 27, 2017, 4:30 p.m. UTC 
Hi!

[I was waiting for a comment from Rob for the initial submission,
 but that never came and I nearly forgot. Instead of pinging again,
 I'm resubmitting with the review comment from Guenter fixed, hoping
 that Rob will react this time.]


This is a workaround for a problem in the AT91 I2C adapter driver
(or perhaps the hardware?) when it drives the TWI peripheral on an
Atmel sama5d3 chip as I2C.

Apparently, that driver can delay in excess of 100 ms just after
the transfer of the 7th bit of the last byte. When it does this
the I2C bus, when viewed from SMBUS client devices, appears
stuck with SCL low. Some SMBUS devices times out under these
conditions, in particular temperature sensors. The I2C adapter
driver does however not notice the timeout, and thinks the transfer
completed successfully when it finally desides to finish the
transaction. When this happens, the 8th bit of the last byte is
always set, and thus quite possibly corrupted.

The chip this was observed with (an nxp SE97) has a means to disable
the SMBUS timeout detector, which "fixes" things. Do that.

This should probably go to stable?

Previous discussion: https://lkml.org/lkml/2017/10/12/227

Changes since v1:    https://lkml.org/lkml/2017/10/13/184
- Added #include of bitops.h
- Rebased to v4.15-rc1

Cheers,
Peter

Peter Rosin (2):
  hwmon: (jc42) optionally try to disable the SMBUS timeout
  ARM: dts: at91: disable the nxp,se97b SMBUS timeout on the TSE-850

 Documentation/devicetree/bindings/hwmon/jc42.txt |  4 ++++
 arch/arm/boot/dts/at91-tse850-3.dts              |  1 +
 drivers/hwmon/jc42.c                             | 21 +++++++++++++++++++++
 3 files changed, 26 insertions(+)

Comments

Guenter Roeck Nov. 29, 2017, 8:53 p.m. UTC | #1 
On Mon, Nov 27, 2017 at 05:31:01PM +0100, Peter Rosin wrote:
> The I2C adapter driver is sometimes slow, causing the SCL line to
> be stuck low for more than the stipulated SMBUS timeout of 25-35 ms.
> This causes the client device to give up which in turn causes silent
> corruption of data. So, disable the SMBUS timeout in the client device.
> 
> Signed-off-by: Peter Rosin <peda@axentia.se>

Acked-by: Guenter Roeck <linux@roeck-us.net>

I assume this will be sent upstream through an arm tree.

Thanks,
Guenter

> ---
>  arch/arm/boot/dts/at91-tse850-3.dts | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/boot/dts/at91-tse850-3.dts b/arch/arm/boot/dts/at91-tse850-3.dts
> index 5f29010cdbd8..9b82cc8843e1 100644
> --- a/arch/arm/boot/dts/at91-tse850-3.dts
> +++ b/arch/arm/boot/dts/at91-tse850-3.dts
> @@ -221,6 +221,7 @@
>  	jc42@18 {
>  		compatible = "nxp,se97b", "jedec,jc-42.4-temp";
>  		reg = <0x18>;
> +		smbus-timeout-disable;
>  	};
>  
>  	dpot: mcp4651-104@28 {
> -- 
> 2.11.0
> 
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Alexandre Belloni Nov. 29, 2017, 8:56 p.m. UTC | #2 
On 29/11/2017 at 12:53:11 -0800, Guenter Roeck wrote:
> On Mon, Nov 27, 2017 at 05:31:01PM +0100, Peter Rosin wrote:
> > The I2C adapter driver is sometimes slow, causing the SCL line to
> > be stuck low for more than the stipulated SMBUS timeout of 25-35 ms.
> > This causes the client device to give up which in turn causes silent
> > corruption of data. So, disable the SMBUS timeout in the client device.
> > 
> > Signed-off-by: Peter Rosin <peda@axentia.se>
> 
> Acked-by: Guenter Roeck <linux@roeck-us.net>
> 
> I assume this will be sent upstream through an arm tree.
> 

Yes, I'm applying it right now.

> Thanks,
> Guenter
> 
> > ---
> >  arch/arm/boot/dts/at91-tse850-3.dts | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/arm/boot/dts/at91-tse850-3.dts b/arch/arm/boot/dts/at91-tse850-3.dts
> > index 5f29010cdbd8..9b82cc8843e1 100644
> > --- a/arch/arm/boot/dts/at91-tse850-3.dts
> > +++ b/arch/arm/boot/dts/at91-tse850-3.dts
> > @@ -221,6 +221,7 @@
> >  	jc42@18 {
> >  		compatible = "nxp,se97b", "jedec,jc-42.4-temp";
> >  		reg = <0x18>;
> > +		smbus-timeout-disable;
> >  	};
> >  
> >  	dpot: mcp4651-104@28 {
> > -- 
> > 2.11.0
> >
Guenter Roeck Nov. 30, 2017, 5:16 p.m. UTC | #3 
On Wed, Nov 29, 2017 at 09:56:29PM +0100, Alexandre Belloni wrote:
> On 29/11/2017 at 12:53:11 -0800, Guenter Roeck wrote:
> > On Mon, Nov 27, 2017 at 05:31:01PM +0100, Peter Rosin wrote:
> > > The I2C adapter driver is sometimes slow, causing the SCL line to
> > > be stuck low for more than the stipulated SMBUS timeout of 25-35 ms.
> > > This causes the client device to give up which in turn causes silent
> > > corruption of data. So, disable the SMBUS timeout in the client device.
> > > 
> > > Signed-off-by: Peter Rosin <peda@axentia.se>
> > 
> > Acked-by: Guenter Roeck <linux@roeck-us.net>
> > 
> > I assume this will be sent upstream through an arm tree.
> > 
> 
> Yes, I'm applying it right now.
> 
Are you going to apply the patch for 4.15, or queue it up for 4.16 ?
I have been arguing with myself if this is a feature or a bug fix.
So far I queued the driver change up for 4.16, but I am open to
applying it to 4.15. Any thoughts ?

Guenter

> > Thanks,
> > Guenter
> > 
> > > ---
> > >  arch/arm/boot/dts/at91-tse850-3.dts | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/arch/arm/boot/dts/at91-tse850-3.dts b/arch/arm/boot/dts/at91-tse850-3.dts
> > > index 5f29010cdbd8..9b82cc8843e1 100644
> > > --- a/arch/arm/boot/dts/at91-tse850-3.dts
> > > +++ b/arch/arm/boot/dts/at91-tse850-3.dts
> > > @@ -221,6 +221,7 @@
> > >  	jc42@18 {
> > >  		compatible = "nxp,se97b", "jedec,jc-42.4-temp";
> > >  		reg = <0x18>;
> > > +		smbus-timeout-disable;
> > >  	};
> > >  
> > >  	dpot: mcp4651-104@28 {
> > > -- 
> > > 2.11.0
> > > 
> 
> -- 
> Alexandre Belloni, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com
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Alexandre Belloni Nov. 30, 2017, 5:26 p.m. UTC | #4 
On 30/11/2017 at 09:16:38 -0800, Guenter Roeck wrote:
> On Wed, Nov 29, 2017 at 09:56:29PM +0100, Alexandre Belloni wrote:
> > On 29/11/2017 at 12:53:11 -0800, Guenter Roeck wrote:
> > > On Mon, Nov 27, 2017 at 05:31:01PM +0100, Peter Rosin wrote:
> > > > The I2C adapter driver is sometimes slow, causing the SCL line to
> > > > be stuck low for more than the stipulated SMBUS timeout of 25-35 ms.
> > > > This causes the client device to give up which in turn causes silent
> > > > corruption of data. So, disable the SMBUS timeout in the client device.
> > > > 
> > > > Signed-off-by: Peter Rosin <peda@axentia.se>
> > > 
> > > Acked-by: Guenter Roeck <linux@roeck-us.net>
> > > 
> > > I assume this will be sent upstream through an arm tree.
> > > 
> > 
> > Yes, I'm applying it right now.
> > 
> Are you going to apply the patch for 4.15, or queue it up for 4.16 ?
> I have been arguing with myself if this is a feature or a bug fix.
> So far I queued the driver change up for 4.16, but I am open to
> applying it to 4.15. Any thoughts ?
> 

I was wondering that myself. I'm open to have it as a fix in 4.15. Or
maybe Peter can send the series to stable if he needs it in 4.14.

Peter, what do you think/want?
Peter Rosin Nov. 30, 2017, 6:46 p.m. UTC | #5 
On 2017-11-30 18:26, Alexandre Belloni wrote:
> On 30/11/2017 at 09:16:38 -0800, Guenter Roeck wrote:
>> On Wed, Nov 29, 2017 at 09:56:29PM +0100, Alexandre Belloni wrote:
>>> On 29/11/2017 at 12:53:11 -0800, Guenter Roeck wrote:
>>>> On Mon, Nov 27, 2017 at 05:31:01PM +0100, Peter Rosin wrote:
>>>>> The I2C adapter driver is sometimes slow, causing the SCL line to
>>>>> be stuck low for more than the stipulated SMBUS timeout of 25-35 ms.
>>>>> This causes the client device to give up which in turn causes silent
>>>>> corruption of data. So, disable the SMBUS timeout in the client device.
>>>>>
>>>>> Signed-off-by: Peter Rosin <peda@axentia.se>
>>>>
>>>> Acked-by: Guenter Roeck <linux@roeck-us.net>
>>>>
>>>> I assume this will be sent upstream through an arm tree.
>>>>
>>>
>>> Yes, I'm applying it right now.
>>>
>> Are you going to apply the patch for 4.15, or queue it up for 4.16 ?
>> I have been arguing with myself if this is a feature or a bug fix.
>> So far I queued the driver change up for 4.16, but I am open to
>> applying it to 4.15. Any thoughts ?
>>
> 
> I was wondering that myself. I'm open to have it as a fix in 4.15. Or
> maybe Peter can send the series to stable if he needs it in 4.14.
> 
> Peter, what do you think/want?

TL;DR Either way is fine.

I think it's a bugfix; it fixes real problems where the application
misbehave due to faulty content when reading from an eeprom. I'm
expecting to make a new release for the hw in question RSN and these
are the only local patches. So, it would be nice if they made it to
4.14.x before my release happens. However, it's not like it's difficult
to rebase the patches should that backport not happen or take too long.

The badness started to happen much more frequently due to some timing
difference affecting the i2c bus driver, but in theory it's a problem
that has been there from the start. I have just not noticed it before...

Cheers,
Peter
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Guenter Roeck Nov. 30, 2017, 9:17 p.m. UTC | #6 
On Thu, Nov 30, 2017 at 07:46:09PM +0100, Peter Rosin wrote:
> On 2017-11-30 18:26, Alexandre Belloni wrote:
> > On 30/11/2017 at 09:16:38 -0800, Guenter Roeck wrote:
> >> On Wed, Nov 29, 2017 at 09:56:29PM +0100, Alexandre Belloni wrote:
> >>> On 29/11/2017 at 12:53:11 -0800, Guenter Roeck wrote:
> >>>> On Mon, Nov 27, 2017 at 05:31:01PM +0100, Peter Rosin wrote:
> >>>>> The I2C adapter driver is sometimes slow, causing the SCL line to
> >>>>> be stuck low for more than the stipulated SMBUS timeout of 25-35 ms.
> >>>>> This causes the client device to give up which in turn causes silent
> >>>>> corruption of data. So, disable the SMBUS timeout in the client device.
> >>>>>
> >>>>> Signed-off-by: Peter Rosin <peda@axentia.se>
> >>>>
> >>>> Acked-by: Guenter Roeck <linux@roeck-us.net>
> >>>>
> >>>> I assume this will be sent upstream through an arm tree.
> >>>>
> >>>
> >>> Yes, I'm applying it right now.
> >>>
> >> Are you going to apply the patch for 4.15, or queue it up for 4.16 ?
> >> I have been arguing with myself if this is a feature or a bug fix.
> >> So far I queued the driver change up for 4.16, but I am open to
> >> applying it to 4.15. Any thoughts ?
> >>
> > 
> > I was wondering that myself. I'm open to have it as a fix in 4.15. Or
> > maybe Peter can send the series to stable if he needs it in 4.14.
> > 
> > Peter, what do you think/want?
> 
> TL;DR Either way is fine.
> 
> I think it's a bugfix; it fixes real problems where the application
> misbehave due to faulty content when reading from an eeprom. I'm
> expecting to make a new release for the hw in question RSN and these
> are the only local patches. So, it would be nice if they made it to
> 4.14.x before my release happens. However, it's not like it's difficult
> to rebase the patches should that backport not happen or take too long.
> 
Good enough for me. I'll send it as a fix for v4.15, with Cc: stable.

Guenter

> The badness started to happen much more frequently due to some timing
> difference affecting the i2c bus driver, but in theory it's a problem
> that has been there from the start. I have just not noticed it before...
> 
> Cheers,
> Peter
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Alexandre Belloni Dec. 4, 2017, 7:39 p.m. UTC | #7 
On 30/11/2017 at 13:17:40 -0800, Guenter Roeck wrote:
> > I think it's a bugfix; it fixes real problems where the application
> > misbehave due to faulty content when reading from an eeprom. I'm
> > expecting to make a new release for the hw in question RSN and these
> > are the only local patches. So, it would be nice if they made it to
> > 4.14.x before my release happens. However, it's not like it's difficult
> > to rebase the patches should that backport not happen or take too long.
> > 
> Good enough for me. I'll send it as a fix for v4.15, with Cc: stable.
> 

I have it in my fixes branch too, I'll send it to arm-soc soon.