Re: [PATCH] drm/bridge: panel: Check device dependency before managing device link

[Ville Syrjälä]

On Thu, Nov 23, 2023 at 11:26:15AM +0800, Liu Ying wrote:
> Some panel devices already depend on DRM device, like the panel in
> arch/arm/boot/dts/st/ste-ux500-samsung-skomer.dts, because DRM device is
> the ancestor of those panel devices.  device_link_add() would fail by
> returning a NULL pointer for those panel devices because of the existing
> dependency.  So, check the dependency by calling device_is_dependent()
> before adding or deleting device link between panel device and DRM device
> so that the link is managed only for independent panel devices.
> 
> Fixes: 887878014534 ("drm/bridge: panel: Fix device link for DRM_BRIDGE_ATTACH_NO_CONNECTOR")
> Fixes: 199cf07ebd2b ("drm/bridge: panel: Add a device link between drm device and panel device")
> Reported-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/CACRpkdaGzXD6HbiX7mVUNJAJtMEPG00Pp6+nJ1P0JrfJ-ArMvQ@xxxxxxxxxxxxxx/T/
> Tested-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Signed-off-by: Liu Ying <victor.liu@xxxxxxx>
> ---
>  drivers/gpu/drm/bridge/panel.c | 27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
> index e48823a4f1ed..5e8980023407 100644
> --- a/drivers/gpu/drm/bridge/panel.c
> +++ b/drivers/gpu/drm/bridge/panel.c
> @@ -23,6 +23,7 @@ struct panel_bridge {
>  	struct drm_panel *panel;
>  	struct device_link *link;
>  	u32 connector_type;
> +	bool is_independent;
>  };
>  
>  static inline struct panel_bridge *
> @@ -67,12 +68,17 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
>  	struct drm_device *drm_dev = bridge->dev;
>  	int ret;
>  
> -	panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
> -					     DL_FLAG_STATELESS);
> -	if (!panel_bridge->link) {
> -		DRM_ERROR("Failed to add device link between %s and %s\n",
> -			  dev_name(drm_dev->dev), dev_name(panel->dev));
> -		return -EINVAL;
> +	panel_bridge->is_independent = !device_is_dependent(drm_dev->dev,
> +							    panel->dev);

This broke the build. Looks like device_is_dependent() is not even exported.
ERROR: modpost: "device_is_dependent" [drivers/gpu/drm/drm_kms_helper.ko] undefined!

The recommended defconfigs in rerere-cache do seem to have CONFIG_DRM_KMS_HELPER=m
so this should have been caught before pushing. How did it slip through?

> +
> +	if (panel_bridge->is_independent) {
> +		panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
> +						     DL_FLAG_STATELESS);
> +		if (!panel_bridge->link) {
> +			DRM_ERROR("Failed to add device link between %s and %s\n",
> +				  dev_name(drm_dev->dev), dev_name(panel->dev));
> +			return -EINVAL;
> +		}
>  	}
>  
>  	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
> @@ -80,7 +86,8 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
>  
>  	if (!bridge->encoder) {
>  		DRM_ERROR("Missing encoder\n");
> -		device_link_del(panel_bridge->link);
> +		if (panel_bridge->is_independent)
> +			device_link_del(panel_bridge->link);
>  		return -ENODEV;
>  	}
>  
> @@ -92,7 +99,8 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
>  				 panel_bridge->connector_type);
>  	if (ret) {
>  		DRM_ERROR("Failed to initialize connector\n");
> -		device_link_del(panel_bridge->link);
> +		if (panel_bridge->is_independent)
> +			device_link_del(panel_bridge->link);
>  		return ret;
>  	}
>  
> @@ -115,7 +123,8 @@ static void panel_bridge_detach(struct drm_bridge *bridge)
>  	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
>  	struct drm_connector *connector = &panel_bridge->connector;
>  
> -	device_link_del(panel_bridge->link);
> +	if (panel_bridge->is_independent)
> +		device_link_del(panel_bridge->link);
>  
>  	/*
>  	 * Cleanup the connector if we know it was initialized.
> -- 
> 2.37.1

-- 
Ville Syrjälä
Intel