Re: [PATCH RESEND v4 3/3] drm/bridge: sii9234: use extcon cable detection logic to detect MHL

On Tue, 02 Jun 2026 20:36:50 +0200, Henrik Grimler <[email protected]> wrote:

Hello Henrik,

> To use MHL we currently need the MHL chip to be permanently on, which
> consumes unnecessary power. Let's use extcon attached to MUIC to enable
> the MHL chip only if it detects an MHL cable.
> 
> Tested-by: Marek Szyprowski <[email protected]>
> Signed-off-by: Henrik Grimler <[email protected]>

I have several minor comments, but overall looks OK to me.

>
>
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index 4a57d49b4c6d..11171b4054b5 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -333,6 +333,7 @@ config DRM_SII902X
>  config DRM_SII9234
>  	tristate "Silicon Image SII9234 HDMI/MHL bridge"
>  	depends on OF
> +	depends on EXTCON || !EXTCON

IMO the other syntax is more readable:

          depends on EXTCON if EXTCON

See https://www.kernel.org/doc/html/latest/kbuild/kconfig-language.html

>
> diff --git a/drivers/gpu/drm/bridge/sii9234.c b/drivers/gpu/drm/bridge/sii9234.c
> index e43248e515b3..72c6aeed6e12 100644
> --- a/drivers/gpu/drm/bridge/sii9234.c
> +++ b/drivers/gpu/drm/bridge/sii9234.c
> @@ -170,8 +172,12 @@ struct sii9234 {
>  	struct drm_bridge bridge;
>  	struct device *dev;
>  	struct gpio_desc *gpio_reset;
> -	int i2c_error;
>  	struct regulator_bulk_data supplies[4];
> +	struct extcon_dev *extcon;
> +	struct notifier_block extcon_nb;
> +	struct work_struct extcon_wq;
> +	int cable_state;
> +	int i2c_error;

Moving i2c_error is unrelated, and apparently unneeded unless I'm missing
something.

> @@ -863,6 +869,70 @@ static int sii9234_init_resources(struct sii9234 *ctx,
>  	return 0;
>  }
>  
> +static void sii9234_extcon_work(struct work_struct *work)
> +{
> +	struct sii9234 *ctx =
> +		container_of(work, struct sii9234, extcon_wq);

Can fit on a single line.

> +	int state = extcon_get_state(ctx->extcon, EXTCON_DISP_MHL);
> +
> +	if (state == ctx->cable_state)
> +		return;
> +
> +	ctx->cable_state = state;
> +
> +	if (state > 0)
> +		sii9234_cable_in(ctx);
> +	else
> +		sii9234_cable_out(ctx);
> +}
> +
> +static int sii9234_extcon_notifier(struct notifier_block *self,

"self" is not a very descriptive name. What about "nb", being a notifier
block?

> +			unsigned long event, void *ptr)
> +{
> +	struct sii9234 *ctx =
> +		container_of(self, struct sii9234, extcon_nb);

Single line here too.

> [ ... skip 14 lines ... ]
> +	/* Then get micro-USB Interface Controller node */
> +	muic = of_get_next_parent(musb);
> +
> +	if (!muic) {
> +		dev_info(ctx->dev,
> +			 "no extcon found, switching to 'always on' mode\n");

Can fit in a line.

> +		return 0;
> +	}
> +
> +	edev = extcon_find_edev_by_node(muic);
> +	of_node_put(muic);
> +	if (IS_ERR(edev)) {
> +		return dev_err_probe(ctx->dev, PTR_ERR(edev),
> +			      "invalid or missing extcon\n");
> +	}

You can drop the curly braces, and perhaps the dev_err_probe() can fit in a
100-chars line.

> +
> +	ctx->extcon = edev;
> +	ctx->extcon_nb.notifier_call = sii9234_extcon_notifier;
> +	INIT_WORK(&ctx->extcon_wq, sii9234_extcon_work);
> +	ret = extcon_register_notifier(edev, EXTCON_DISP_MHL, &ctx->extcon_nb);
> +	if (ret) {
> +		dev_err(ctx->dev, "failed to register notifier for MHL\n");
> +		return ret;
> +	}

Use dev_err_probe(), and so remove the {}.

> @@ -929,7 +1004,15 @@ static void sii9234_remove(struct i2c_client *client)
>  {
>  	struct sii9234 *ctx = i2c_get_clientdata(client);
>  
> -	sii9234_cable_out(ctx);
> +	if (ctx->extcon) {
> +		extcon_unregister_notifier(ctx->extcon, EXTCON_DISP_MHL,
> +					   &ctx->extcon_nb);

I guess you can use devm_extcon_register_notifier() to simplify a bit the
code.

> +		flush_work(&ctx->extcon_wq);
> +		if (ctx->cable_state > 0)
> +			sii9234_cable_out(ctx);
> +	} else {
> +		sii9234_cable_out(ctx);
> +	}
>  	drm_bridge_remove(&ctx->bridge);
>  }
>  

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com