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

[Andreas Naumann <dev@andin.de>]

Hi,

Am 28.11.2013 17:04, schrieb Nikita Kiryanov:
> 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@denx.de>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Cc: Tom Rini <trini@ti.com>
> Cc: Lubomir Popov <lpopov@mm-sol.com>
> Cc: Enric Balletbo Serra <eballetbo@gmail.com>
> Signed-off-by: Nikita Kiryanov <nikita@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).

I can also confirm this patch eliminates the frequent occurence of the 
following message:
	i2c_write: pads on bus 0 probably not configured (status=0x10)
	Could not write grp_sel to reg 82 (2)

Tested on a custom AM37xx board with 2013.07. Before the patch I got 
this message on about 5% of all reboots (I have test data of several 
thousand reboots). However, the board never failed to boot, with or 
without patch.

cheers,
Andi