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

[Ben Dooks <ben-SMNkleLxa3Z6Wcw2j4pizdi2O/JbrIOy@public.gmane.org>]

On Fri, Sep 24, 2010 at 07:37:03AM -0700, Kevin Hilman wrote:
> "Sudhakar Rajashekhara" <sudhakar.raj-l0cyMroinI0@public.gmane.org> writes:
> 
> > 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>
> >> ---
> >
> > Tested-by: Sudhakar Rajashekhara <sudhakar.raj-l0cyMroinI0@public.gmane.org>
> >
> > Tested with audio loopback on OMAP-L138, OMAP-L137 and DM365. Also tested with
> > i2cdetect function which probes all the devices on the i2c bus.
> 
> 
> Ben, can you queue this one for 2.6.37 with the addition of:

If it is a worthwhile bugfix i'll send it for the next -rc.
 
> 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>
> 
> Thanks,
> 
> Kevin
> 

-- 
-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.