Re: [PATCH] I2C: Fix twl4030 timeouts on omap3430

[Tony Lindgren <tony@atomide.com>]

* Tony Lindgren <tony@atomide.com> [080328 10:41]:
> Hi all,
> 
> This helps with the annoying I2C timeouts. Does anybody have an idea
> why the twl4030 chip does not like doing multiple transfers in a row?
> 
> To me the only difference seems to be that clocks are idled between
> writing the twl4030 register and reading the register value.

I'll push this today with a REVISIT comment added.

Tony


> From 25c4c8f449819cb6f40b59ed1a9b25ebcc7cd72e Mon Sep 17 00:00:00 2001
> From: Tony Lindgren <tony@atomide.com>
> Date: Thu, 27 Mar 2008 19:05:30 +0200
> Subject: [PATCH] I2C: Fix twl4030 timeouts on omap3430
> 
> For some reason doing a twl4030 write-read cycle can hang the I2C bus
> on omap3430. And doing the write and read separately in twl4030_i2c_read()
> seems to fix the problem...
> 
> Not intended for applying, just a temporary workaround.
> 
> diff --git a/drivers/i2c/chips/twl4030-core.c b/drivers/i2c/chips/twl4030-core.c
> index ded86e7..62868b0 100644
> --- a/drivers/i2c/chips/twl4030-core.c
> +++ b/drivers/i2c/chips/twl4030-core.c
> @@ -327,6 +327,7 @@ int twl4030_i2c_read(u8 mod_no, u8 * value, u8 reg, u8 num_bytes)
>  		return -EPERM;
>  	}
>  	mutex_lock(&twl->xfer_lock);
> +
>  	/* [MSG1] fill the register address data */
>  	msg = &twl->xfer_msg[0];
>  	msg->addr = twl->address;
> @@ -334,18 +335,25 @@ int twl4030_i2c_read(u8 mod_no, u8 * value, u8 reg, u8 num_bytes)
>  	msg->flags = 0;	/* Read the register value */
>  	val = twl4030_map[mod_no].base + reg;
>  	msg->buf = &val;
> +	ret = i2c_transfer(twl->client.adapter, twl->xfer_msg, 1);
> +	if (ret < 0)
> +		goto out;
> + 
>  	/* [MSG2] fill the data rx buffer */
>  	msg = &twl->xfer_msg[1];
>  	msg->addr = twl->address;
>  	msg->flags = I2C_M_RD;	/* Read the register value */
>  	msg->len = num_bytes;	/* only n bytes */
>  	msg->buf = value;
> -	ret = i2c_transfer(twl->client.adapter, twl->xfer_msg, 2);
> +	ret = i2c_transfer(twl->client.adapter, twl->xfer_msg, 1);
> +
> +out:
>  	mutex_unlock(&twl->xfer_lock);
>  
>  	/* i2cTransfer returns num messages.translate it pls.. */
>  	if (ret >= 0)
>  		ret = 0;
> +
>  	return ret;
>  }
>