Re: [PATCH v2 3/3] drm/bridge: sii9234: use extcon cable detection logic to detect MHL

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 24.07.2025 20:50, Henrik Grimler wrote:
> 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.
>
> Signed-off-by: Henrik Grimler <henrik@grimler.se>
> ---
> v2: add dependency on extcon. Issue reported by kernel test robot
>      <lkp@intel.com>
> ---
>   drivers/gpu/drm/bridge/Kconfig   |  1 +
>   drivers/gpu/drm/bridge/sii9234.c | 89 ++++++++++++++++++++++++++++++++++++++--
>   2 files changed, 87 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index b9e0ca85226a603a24f90c6879d1499f824060cb..f18a083f6e1c6fe40bde5e65a1548acc61a162ae 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -303,6 +303,7 @@ config DRM_SII902X
>   config DRM_SII9234
>   	tristate "Silicon Image SII9234 HDMI/MHL bridge"
>   	depends on OF
> +	select EXTCON
>   	help
>   	  Say Y here if you want support for the MHL interface.
>   	  It is an I2C driver, that detects connection of MHL bridge
> diff --git a/drivers/gpu/drm/bridge/sii9234.c b/drivers/gpu/drm/bridge/sii9234.c
> index 0e0bb1bf71fdcef788715cfd6fa158a6992def33..4d84ba01ea76816bebdbc29d48a041c9c6cd508e 100644
> --- a/drivers/gpu/drm/bridge/sii9234.c
> +++ b/drivers/gpu/drm/bridge/sii9234.c
> @@ -19,6 +19,7 @@
>   
>   #include <linux/delay.h>
>   #include <linux/err.h>
> +#include <linux/extcon.h>
>   #include <linux/gpio/consumer.h>
>   #include <linux/i2c.h>
>   #include <linux/interrupt.h>
> @@ -26,6 +27,7 @@
>   #include <linux/kernel.h>
>   #include <linux/module.h>
>   #include <linux/mutex.h>
> +#include <linux/of_graph.h>
>   #include <linux/regulator/consumer.h>
>   #include <linux/slab.h>
>   
> @@ -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;
>   
>   	struct mutex lock; /* Protects fields below and device registers */
>   	enum sii9234_state state;
> @@ -864,6 +870,70 @@ 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);
> +	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,
> +			unsigned long event, void *ptr)
> +{
> +	struct sii9234 *ctx =
> +		container_of(self, struct sii9234, extcon_nb);
> +
> +	schedule_work(&ctx->extcon_wq);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static int sii9234_extcon_init(struct sii9234 *ctx)
> +{
> +	struct extcon_dev *edev;
> +	struct device_node *musb, *muic;
> +	int ret;
> +
> +	/* Get micro-USB connector node */
> +	musb = of_graph_get_remote_node(ctx->dev->of_node, 1, -1);
> +	/* 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");
> +		return 0;
> +	}
> +
> +	edev = extcon_find_edev_by_node(muic);
> +	of_node_put(muic);
> +	if (IS_ERR(edev)) {
> +		dev_err_probe(ctx->dev, PTR_ERR(edev),
> +			      "invalid or missing extcon\n");
> +	}

It looks that the original logic got lost somehow in the above code 
block, what causes kernel oops if compiled as module and loaded before 
extcon provider. Please handle -EPROBE_DEFER and propagate error value, 
like the original code did in sii8620 driver:

         if (IS_ERR(edev)) {
                 if (PTR_ERR(edev) == -EPROBE_DEFER)
                         return -EPROBE_DEFER;
                 dev_err(ctx->dev, "Invalid or missing extcon\n");
                 return PTR_ERR(edev);
         }


> +
> +	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;
> +	}
> +
> +	return 0;
> +}
> +
>   static enum drm_mode_status sii9234_mode_valid(struct drm_bridge *bridge,
>   					 const struct drm_display_info *info,
>   					 const struct drm_display_mode *mode)
> @@ -916,12 +986,17 @@ static int sii9234_probe(struct i2c_client *client)
>   	if (ret < 0)
>   		return ret;
>   
> +	ret = sii9234_extcon_init(ctx);
> +	if (ret < 0)
> +		return ret;
> +
>   	i2c_set_clientdata(client, ctx);
>   
>   	ctx->bridge.of_node = dev->of_node;
>   	drm_bridge_add(&ctx->bridge);
>   
> -	sii9234_cable_in(ctx);
> +	if (!ctx->extcon)
> +		sii9234_cable_in(ctx);
>   
>   	return 0;
>   }
> @@ -930,7 +1005,15 @@ 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);
> +		flush_work(&ctx->extcon_wq);
> +		if (ctx->cable_state > 0)
> +			sii9234_cable_out(ctx);
> +	} else {
> +		sii9234_cable_out(ctx);
> +	}
>   	drm_bridge_remove(&ctx->bridge);
>   }
>   
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland