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

Jagan Teki
2021-07-22T07:49:49Z

Hi Maxime,

On Tue, Jul 20, 2021 at 7:15 PM Maxime Ripard <maxime@cerno.tech> 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.

Correct, but drm_of_find_panel_or_bridge is still required in some DSI
drivers where the panel pointer required separately.

>
> 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
> + * @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);
> + }
> +
> + of_node_put(remote);
> +
> + return devm_drm_panel_bridge_add(dev, panel);
> +}

This is ideally similar to drm_of_find_panel_or_bridge followed by
panel_bridge_add. Can we reuse drm_of_find_panel_or_bridge for now
till it deprecated?

Thanks,
Jagan.