[PATCH RFC/RFT 2/3] i2c: omap24xx_i2c: support CONFIG_I2C_REPEATED_START in DM_I2C xfer

[Heiko Schocher]

Hello Aniket,

On 04.03.25 23:04, Aniket Limaye wrote:
> Repeated Start Condition (Sr) can be used to transfer multiple i2c msgs
> without sending a Stop condition (P). So far, the driver default was to
> always send a Stop condition after every i2c msg.
> 
> Add support for a config option (CONFIG_I2C_REPEATED_START) to disable
> sending the Stop condition by default. If this config is enabled, Stop
> condition will be sent only if explicitly requested in the msg flags OR
> if it is the last msg in the transfer.
> 
> Consequently, handle the Repeated Start condition (Sr) in the next msg
> by not calling the wait_for_bb() check since it will simply timeout in
> the absence of a stop condition (BB will be 1 until Stop is programmed)
> 
> Signed-off-by: Aniket Limaye <a-limaye at ti.com>
> ---
>   drivers/i2c/omap24xx_i2c.c | 22 ++++++++++++++++------
>   1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/omap24xx_i2c.c b/drivers/i2c/omap24xx_i2c.c
> index 0d044121d27..d3256ab666d 100644
> --- a/drivers/i2c/omap24xx_i2c.c
> +++ b/drivers/i2c/omap24xx_i2c.c
> @@ -1074,21 +1074,31 @@ static int omap_i2c_xfer(struct udevice *bus, struct i2c_msg *msg, int nmsgs)
>   	u16 i2c_con_reg = 0;
>   
>   	debug("i2c_xfer: %d messages\n", nmsgs);
> -	for (; nmsgs > 0; nmsgs--, msg++) {
> +	for (int i = 0; i < nmsgs; i++, msg++) {
>   		debug("i2c_xfer: chip=0x%x, len=0x%x, read=0x%x\n",
>   		      msg->addr, msg->len, (msg->flags & I2C_M_RD));
>   
> -		/* Wait until bus not busy */
> -		if (wait_for_bb(priv->regs, priv->ip_rev, priv->waitdelay))
> -			return -EREMOTEIO;
> +		/* If previous msg sent a Stop or if this is the first msg
> +		 * Wait until bus not busy
> +		 */

Nitpick: I would like more

		/*
		 * If previous msg sent a Stop or if this is the first msg

but unsure if we have here a strict rule...

> +		if ((i2c_con_reg & I2C_CON_STP) || (i == 0)) {
> +			if (wait_for_bb(priv->regs, priv->ip_rev, priv->waitdelay))
> +				return -EREMOTEIO;
> +		}

You do not need the {} brackets here

>   
> -		/* Set Controller mode with Start and Stop bit */
> -		i2c_con_reg = I2C_CON_EN | I2C_CON_MST | I2C_CON_STT | I2C_CON_STP;
> +		/* Set Controller mode with Start bit */
> +		i2c_con_reg = I2C_CON_EN | I2C_CON_MST | I2C_CON_STT;
>   		/* Set Transmitter/Receiver mode if it is a write/read msg */
>   		if (msg->flags & I2C_M_RD)
>   			i2c_con_reg &= ~I2C_CON_TRX;
>   		else
>   			i2c_con_reg |= I2C_CON_TRX;
> +		/* Send Stop condition (P) by default */
> +		if (!IS_ENABLED(CONFIG_I2C_REPEATED_START))
> +			i2c_con_reg |= I2C_CON_STP;
> +		/* Send Stop if explicitly requested or if this is the last msg */
> +		if ((msg->flags & I2C_M_STOP) || (i == nmsgs - 1))
> +			i2c_con_reg |= I2C_CON_STP;
>   
>   		ret = __omap24_i2c_xfer_msg(priv->regs, priv->ip_rev, priv->waitdelay,
>   					    msg->addr, msg->buf, msg->len,
> 

Thanks!

bye,
Heiko
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