[U-Boot] [PATCH] arm: omap3: i2c: don't zero cnt in i2c_write

[Tom Rini <trini@ti.com>]

On Wed, Nov 27, 2013 at 04:44:09PM +0200, Nikita Kiryanov wrote:
> The zeroing of I2Ci.I2C_CNT register at the end of i2c_write causes
> random I2C failures in OMAP3 based devices. This is probably related
> to the following advisory in OMAP3 errata:
> 
> 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.
> 
> Make the write conditional so that only non-OMAP3 devices will perform it.
> 
> Cc: Heiko Schocher <hs@denx.de>
> Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
> ---
>  drivers/i2c/omap24xx_i2c.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/i2c/omap24xx_i2c.c b/drivers/i2c/omap24xx_i2c.c
> index 3d38c03..2862a8f 100644
> --- a/drivers/i2c/omap24xx_i2c.c
> +++ b/drivers/i2c/omap24xx_i2c.c
> @@ -473,7 +473,10 @@ static int omap24_i2c_write(struct i2c_adapter *adap, uchar chip, uint addr,
>  wr_exit:
>  	flush_fifo(adap);
>  	writew(0xFFFF, &i2c_base->stat);
> +	/* This write is known to cause undefined behavior on OMAP3 */
> +#ifndef CONFIG_OMAP34XX
>  	writew(0, &i2c_base->cnt);
> +#endif
>  	return i2c_error;
>  }

Yay for tracking this down.  Can you please expand the comment to
mention the specific advisory?  Thanks!

-- 
Tom
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