From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH v4] i2c: davinci: Fix race when setting up for TX Date: Thu, 30 Sep 2010 06:10:31 -0700 Message-ID: <87wrq3l6m0.fsf@deeprootsystems.com> References: <4C97CEC9.8060602@boundarydevices.com> <1285042408-13200-1-git-send-email-jon.povey@racelogic.co.uk> <4C9904E6.7070608@boundarydevices.com> <20100922000916.GH7494@trinity.fluff.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <20100922000916.GH7494-SMNkleLxa3Z6Wcw2j4pizdi2O/JbrIOy@public.gmane.org> (Ben Dooks's message of "Wed, 22 Sep 2010 01:09:16 +0100") Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Ben Dooks Cc: Troy Kisky , davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org Ben Dooks 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 >> >> 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 >> > >> > >> > >> 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 Tested-by: Sudhakar Rajashekhara Acked-by: Kevin Hilman