[U-Boot] [PATCH V2] arm: omap: i2c: don't zero cnt in i2c_write

[Thomas Petazzoni]

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 <hs at denx.de>
> Cc: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> Cc: Tom Rini <trini at ti.com>
> Cc: Lubomir Popov <lpopov at mm-sol.com>
> Cc: Enric Balletbo Serra <eballetbo at gmail.com>
> Signed-off-by: Nikita Kiryanov <nikita at compulab.co.il>
> ---
> 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 <thomas.petazzoni at free-electrons.com>

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