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

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

Troy Kisky <troy.kisky-Q5RJGjKts06CY9SHAMCTRUEOCMrvLtNR@public.gmane.org> writes:

> On 9/21/2010 4:24 AM, Sudhakar Rajashekhara wrote:
>> Hi,
>> 
>> On Tue, Sep 21, 2010 at 09:43:28, Jon Povey wrote:
>>> 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>
>>> ---
>>> Reworked after comments by Troy and Sudhakar.
>>>
>>> Looking at the datasheet it seemed like setting STP without STT early
>>> might cause a stray STOP to be generated, so I moved it into the second
>>> MDR load.
>>>
>>> This passes a quick smoke test but I can't do much more testing right at
>>> the moment. Sudhakar, your comments would be welcomed.
>>>
>> 
>> Looks good to me. I can test on couple of platforms I have and update the result
>> by tomorrow.
>> 
>> Thanks,
>> Sudhakar
>> 
>> 
>> 
> I like it too. I hope it works for omap.

Troy, can I take this as an Acked-by from you?  or a Tested-by?

Thanks,

Kevin