Re: [PATCH] i2c: designware: don't infer timings described by ACPI from clock rate

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

On 05/19/2017 01:06 PM, Ard Biesheuvel wrote:
> On 19 May 2017 at 11:01, Jarkko Nikula <jarkko.nikula@linux.intel.com> wrote:
>> On 05/19/2017 11:56 AM, Ard Biesheuvel wrote:
>>>
>>> Commit bd698d24b1b57 ("i2c: designware: Get selected speed mode
>>> sda-hold-time via ACPI") updated the logic that reads the timing
>>> parameters for various I2C bus rates from the DSDT, to only read
>>> the timing parameters for the currently selected mode.
>>>
>>> This causes a WARN_ON() splat on platforms that legally omit the clock
>>> frequency from the ACPI description, because in the new situation, the
>>> core I2C designware driver still accesses the fields in the driver
>>> struct that we no longer populate, and proceeds to calculate them from
>>> the clock frequency. Since the clock frequency is unspecified, the
>>> driver complains loudly using a WARN_ON().
>>>
>>> So revert back to the old situation, where the struct fields for all
>>> timings are populated, but retain the new logic which chooses the SDA
>>> hold time from the timing mode that is currently in use.
>>>
>>> Fixes: bd698d24b1b57 ("i2c: designware: Get selected speed mode ...")
>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>> ---
>>>  drivers/i2c/busses/i2c-designware-platdrv.c | 18 ++++++++++--------
>>>  1 file changed, 10 insertions(+), 8 deletions(-)
>>>
>> Thanks, this is ok to me. Let's add also kudos to Lorenzo:
>>
>> Reported-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>> Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
>
> Thanks. I suppose this is going in as a fix? If not, please cc to -stable
>
That's not needed as the bd698d24b1b57 came during pre 4.12-rc1 cycle. 
But good to get this into 4.12 due probable regression in high-speed 
transfers and to get rid of log spamming.

-- 
Jarkko