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

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

Ben Dooks <ben-i2c-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org> writes:

> On Tue, Sep 21, 2010 at 12:17:58PM -0700, Troy Kisky wrote:
>> 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.
>> 
>> Thanks as well
>> Troy
>
> Ok, any objections to this being applied, or should I wait?

Please apply with:

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>