Re: [PATCH v4] i2c: davinci: Fix race when setting up for TX

[Kevin Hilman <khilman-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org>]

Jon Povey <Jon.Povey-Ean/AyPsLtfkYMGBc/C6ZA@public.gmane.org> writes:

> Hi Ben,
>
> I am not on the i2c list but noticed this pull request:
> http://www.spinics.net/linux/lists/linux-i2c/msg04022.html
>
> I think you have the wrong (old) version of this patch in that branch,
> http://git.fluff.org/gitweb?p=bjdooks/linux.git;a=commitdiff;h=4bba0fd8d1c6d405df666e2573e1a1f917098be0
>
> The correct v4 one from the start of this thread has more lines
> of patch and this commit message:

It is also available in my davinci-i2c branch:
git://git.kernel.org/pub/scm/linux/kernel/git/khilman/linux-davinci.git davinci-i2c

Thanks Jon for catching this,

Kevin

>>>>>> When setting up to transmit, a race exists between the ISR and
>>>>>> i2c_davinci_xfer_msg() trying to load the first byte and adjust
>>>>>> counters. This is mostly visible for transmits > 1 byte long.
>>>>>>
>>>>>> The hardware starts sending immediately that MDR.STT is set. IMR
>>>>>> trickery doesn't work because if we start sending, finish the
>>>>>> first byte and an XRDY event occurs before we load IMR to unmask
>>>>>> it, we never get an interrupt, and we timeout.
>>>>>>
>>>>>> Sudhakar Rajashekhara explains that at least OMAP-L138 requires
>>>>>> MDR mode settings before DXR for correct behaviour, so load MDR
>>>>>> first with STT cleared and later load again with STT set.
>>>>>>
>>>>>> Tested on DM355 connected to Techwell TW2836 and Wolfson WM8985
>>>>>>
>>>>>> Signed-off-by: Jon Povey <jon.povey-Ean/AyPsLtfkYMGBc/C6ZA@public.gmane.org>
>>>>>> CC: Sudhakar Rajashekhara <sudhakar.raj-l0cyMroinI0@public.gmane.org>
>>>>>> CC: Troy Kisky <troy.kisky-Q5RJGjKts06CY9SHAMCTRUEOCMrvLtNR@public.gmane.org>
>
> It also has some more acks and a tested, via Kevin:
>
>> Acked-by: Troy Kisky <troy.kisky-Q5RJGjKts06CY9SHAMCTRUEOCMrvLtNR@public.gmane.org>
>> Tested-by: Sudhakar Rajashekhara <sudhakar.raj-l0cyMroinI0@public.gmane.org>
>> Acked-by: Kevin Hilman <khilman-1D3HCaltpLuhEniVeURVKkEOCMrvLtNR@public.gmane.org>
>
>
> --
> Jon Povey
> jon.povey-Ean/AyPsLtfkYMGBc/C6ZA@public.gmane.org
>
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