From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Petazzoni Date: Mon, 2 Dec 2013 13:48:46 +0100 Subject: [U-Boot] [PATCH V2] arm: omap: i2c: don't zero cnt in i2c_write In-Reply-To: <1385654682-2775-1-git-send-email-nikita@compulab.co.il> References: <1385563449-15094-1-git-send-email-nikita@compulab.co.il> <1385654682-2775-1-git-send-email-nikita@compulab.co.il> Message-ID: <20131202134846.7e575130@skate> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Dear Nikita Kiryanov, On Thu, 28 Nov 2013 18:04:42 +0200, Nikita Kiryanov wrote: > Writing zero into I2Ci.I2C_CNT register causes random I2C failures in OMAP3 > based devices. This seems to be related to the following advisory which > apears in multiple erratas for OMAP3 SoCs (OMAP35xx, DM37xx), as well as > OMAP4430 TRM: > > Advisory: > I2C Module Does Not Allow 0-Byte Data Requests > Details: > When configured as the master, the I2C module does not allow 0-byte data > transfers. Note: Programming I2Ci.I2C_CNT[15:0]: DCOUNT = 0 will cause > undefined behavior. > Workaround(s): > No workaround. Do not use 0-byte data requests. > > The writes in question are unnecessary from a functional point of view. > Most of them are done after I/O has finished, and the only one that preceds > I/O (in i2c_probe()) is also unnecessary because a stop bit is sent before > actual data transmission takes place. > > Therefore, remove all writes that zero the cnt register. > > Cc: Heiko Schocher > Cc: Thomas Petazzoni > Cc: Tom Rini > Cc: Lubomir Popov > Cc: Enric Balletbo Serra > Signed-off-by: Nikita Kiryanov > --- > Changes in V2: > Removed all instances of writew(0, &i2c_base->cnt) instead of just the > one in i2c_write (following a test of V1 by Thomas Petazzoni). Tested-by: Thomas Petazzoni On IGEPv2, OMAP36XX/37XX-GP ES1.2. Thanks a lot! Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com