linux-kernel - Re: [PATCH v2 2/2] ARM: dts: at91: disable the nxp,se97b SMBUS timeout on the TSE-850

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Date:   Thu, 30 Nov 2017 19:46:09 +0100
From:   Peter Rosin <peda@...ntia.se>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Russell King <linux@...linux.org.uk>,
        Jean Delvare <jdelvare@...e.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v2 2/2] ARM: dts: at91: disable the nxp,se97b SMBUS
 timeout on the TSE-850

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@...ntia.se>
>>>>
>>>> Acked-by: Guenter Roeck <linux@...ck-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