[PATCH 2/2] i2c: mt7621: limit SCL_STRETCH only to Mediatek SoC

[Rob Herring]

On Wed, Oct 21, 2026 at 05:39:52PM +0200, Christian Marangi wrote:
> The same I2C driver is also used for Airoha SoC with the only difference
> that the i2c_reset should not enable SCL_STRETCH for Airoha SoC.
> 
> Introduce a new compatible for Airoha and limit the SCL_STRETCH only to
> Mediatek SoC.
> 
> Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
> ---
>  drivers/i2c/busses/i2c-mt7621.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-mt7621.c b/drivers/i2c/busses/i2c-mt7621.c
> index 0a288c998419..19dde7c4069e 100644
> --- a/drivers/i2c/busses/i2c-mt7621.c
> +++ b/drivers/i2c/busses/i2c-mt7621.c
> @@ -65,6 +65,7 @@ struct mtk_i2c {
>  	u32 clk_div;
>  	u32 flags;
>  	struct clk *clk;
> +	bool have_scl_stretch;
>  };
>  
>  static int mtk_i2c_wait_idle(struct mtk_i2c *i2c)
> @@ -83,6 +84,7 @@ static int mtk_i2c_wait_idle(struct mtk_i2c *i2c)
>  
>  static void mtk_i2c_reset(struct mtk_i2c *i2c)
>  {
> +	u32 reg;
>  	int ret;
>  
>  	ret = device_reset(i2c->adap.dev.parent);
> @@ -93,8 +95,11 @@ static void mtk_i2c_reset(struct mtk_i2c *i2c)
>  	 * Don't set SM0CTL0_ODRAIN as its bit meaning is inverted. To
>  	 * configure open-drain mode, this bit needs to be cleared.
>  	 */
> -	iowrite32(((i2c->clk_div << 16) & SM0CTL0_CLK_DIV_MASK) | SM0CTL0_EN |
> -		  SM0CTL0_SCL_STRETCH, i2c->base + REG_SM0CTL0_REG);
> +	reg = ((i2c->clk_div << 16) & SM0CTL0_CLK_DIV_MASK) | SM0CTL0_EN;
> +	if (i2c->have_scl_stretch)
> +		reg |= SM0CTL0_SCL_STRETCH;
> +
> +	iowrite32(reg, i2c->base + REG_SM0CTL0_REG);
>  	iowrite32(0, i2c->base + REG_SM0CFG2_REG);
>  }
>  
> @@ -249,6 +254,7 @@ static const struct i2c_algorithm mtk_i2c_algo = {
>  
>  static const struct of_device_id i2c_mtk_dt_ids[] = {
>  	{ .compatible = "mediatek,mt7621-i2c" },
> +	{ .compatible = "airoha,an7581-i2c" },
>  	{ /* sentinel */ }
>  };
>  
> @@ -296,6 +302,10 @@ static int mtk_i2c_probe(struct platform_device *pdev)
>  		return -EINVAL;
>  	}
>  
> +	/* Set SCL_STRETCH only for Mediatek SoC */
> +	if (device_is_compatible(i2c->dev, "mediatek,mt7621-i2c"))
> +		i2c->have_scl_stretch = true;

Add match data for this. Calling device_is_compatible() doesn't scale.

Rob