From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Sudhakar Rajashekhara" Subject: RE: [PATCH v4] i2c: davinci: Fix race when setting up for TX Date: Tue, 21 Sep 2010 16:54:17 +0530 Message-ID: <20601.6880846166$1285068661@news.gmane.org> References: <4C97CEC9.8060602@boundarydevices.com> <1285042408-13200-1-git-send-email-jon.povey@racelogic.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1285042408-13200-1-git-send-email-jon.povey-Ean/AyPsLtfkYMGBc/C6ZA@public.gmane.org> Content-Language: en-us List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: davinci-linux-open-source-bounces+gld-davinci-linux-open-source=gmane.org-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org Errors-To: davinci-linux-open-source-bounces+gld-davinci-linux-open-source=gmane.org-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org To: 'Jon Povey' , davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org 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 > CC: Sudhakar Rajashekhara > CC: Troy Kisky > --- > 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