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@xxxxxxxxxxxxxxx> >> CC: Sudhakar Rajashekhara <sudhakar.raj@xxxxxx> >> CC: Troy Kisky <troy.kisky@xxxxxxxxxxxxxxxxxxx> >> --- >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
