Re: [PATCH 02/10] drm/bridge: Add a function to abstract away panels

[Sam Ravnborg <sam@ravnborg.org>]

Hi Maxime,

On Tue, Jul 20, 2021 at 03:45:17PM +0200, Maxime Ripard wrote:
> Display drivers so far need to have a lot of boilerplate to first
> retrieve either the panel or bridge that they are connected to using
> drm_of_find_panel_or_bridge(), and then either deal with each with ad-hoc
> functions or create a drm panel bridge through drm_panel_bridge_add.
> 
> In order to reduce the boilerplate and hopefully create a path of least
> resistance towards using the DRM panel bridge layer, let's create the
> function devm_drm_of_get_next to reduce that boilerplate.
> 
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---
>  drivers/gpu/drm/drm_bridge.c | 62 +++++++++++++++++++++++++++++++++---
>  drivers/gpu/drm/drm_of.c     |  3 ++
>  include/drm/drm_bridge.h     |  2 ++
>  3 files changed, 63 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 044acd07c153..aef8c9f4fb9f 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -24,10 +24,12 @@
>  #include <linux/err.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> +#include <linux/of_graph.h>
>  
>  #include <drm/drm_atomic_state_helper.h>
>  #include <drm/drm_bridge.h>
>  #include <drm/drm_encoder.h>
> +#include <drm/drm_panel.h>
>  
>  #include "drm_crtc_internal.h"
>  
> @@ -50,10 +52,8 @@
>   *
>   * Display drivers are responsible for linking encoders with the first bridge
>   * in the chains. This is done by acquiring the appropriate bridge with
> - * of_drm_find_bridge() or drm_of_find_panel_or_bridge(), or creating it for a
> - * panel with drm_panel_bridge_add_typed() (or the managed version
> - * devm_drm_panel_bridge_add_typed()). Once acquired, the bridge shall be
> - * attached to the encoder with a call to drm_bridge_attach().
> + * drm_of_get_next(). Once acquired, the bridge shall be attached to the
> + * encoder with a call to drm_bridge_attach().
>   *
>   * Bridges are responsible for linking themselves with the next bridge in the
>   * chain, if any. This is done the same way as for encoders, with the call to
> @@ -1223,6 +1223,60 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np)
>  	return NULL;
>  }
>  EXPORT_SYMBOL(of_drm_find_bridge);
> +
> +/**
> + * devm_drm_of_get_next - Return next bridge in the chain

I would prefer a more IMO descriptive name - something like this:

devm_drm_of_get_bridge - Return a bridge or a panel wrapped as a bridge


> + * @dev: device to tie the bridge lifetime to
> + * @np: device tree node containing encoder output ports
> + * @port: port in the device tree node
> + * @endpoint: endpoint in the device tree node
> + *
> + * Given a DT node's port and endpoint number, finds the connected node
> + * and returns the associated bridge if any, or creates and returns a
> + * drm panel bridge instance if a panel is connected.
> + *
> + * Returns a pointer to the bridge if successful, or an error pointer
> + * otherwise.
> + */
> +struct drm_bridge *devm_drm_of_get_next(struct device *dev,
> +					struct device_node *np,
> +					unsigned int port,
> +					unsigned int endpoint)
> +{
> +	struct device_node *remote;
> +	struct drm_bridge *bridge;
> +	struct drm_panel *panel;
> +
> +	/*
> +	 * of_graph_get_remote_node() produces a noisy error message if port
> +	 * node isn't found and the absence of the port is a legit case here,
> +	 * so at first we silently check whether graph presents in the
> +	 * device-tree node.
> +	 */
> +	if (!of_graph_is_present(np))
> +		return ERR_PTR(-ENODEV);
> +
> +	remote = of_graph_get_remote_node(np, port, endpoint);
> +	if (!remote)
> +		return ERR_PTR(-ENODEV);
> +
> +	bridge = of_drm_find_bridge(remote);
> +	if (bridge) {
> +		of_node_put(remote);
> +		return bridge;
> +	}
> +
> +	panel = of_drm_find_panel(remote);
> +	if (IS_ERR(panel)) {
> +		of_node_put(remote);
> +		return ERR_CAST(panel);
> +	}
Here panel may be NULL which is unhadled, as devm_drm_panel_bridge_add()
will fault if the passed panel pointer is NULL.

	Sam

> +
> +	of_node_put(remote);
> +
> +	return devm_drm_panel_bridge_add(dev, panel);
> +}
> +EXPORT_SYMBOL(devm_drm_of_get_next);
>  #endif
>  
>  MODULE_AUTHOR("Ajay Kumar <ajaykumar.rs@samsung.com>");
> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> index 997b8827fed2..bbbdc4d17ac9 100644
> --- a/drivers/gpu/drm/drm_of.c
> +++ b/drivers/gpu/drm/drm_of.c
> @@ -231,6 +231,9 @@ EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
>   * return either the associated struct drm_panel or drm_bridge device. Either
>   * @panel or @bridge must not be NULL.
>   *
> + * This function is deprecated and should not be used in new drivers. Use
> + * drm_of_get_next() instead.
> + *
>   * Returns zero if successful, or one of the standard error codes if it fails.
>   */
>  int drm_of_find_panel_or_bridge(const struct device_node *np,
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 46bdfa48c413..e16fafc6f37d 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -911,6 +911,8 @@ struct drm_bridge *devm_drm_panel_bridge_add(struct device *dev,
>  struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
>  						   struct drm_panel *panel,
>  						   u32 connector_type);
> +struct drm_bridge *devm_drm_of_get_next(struct device *dev, struct device_node *node,
> +					unsigned int port, unsigned int endpoint);
>  struct drm_connector *drm_panel_bridge_connector(struct drm_bridge *bridge);
>  #endif
>  
> -- 
> 2.31.1