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Date:   Thu, 22 Jul 2021 13:19:32 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Robert Foss <robert.foss@...aro.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Sam Ravnborg <sam@...nborg.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 02/10] drm/bridge: Add a function to abstract away panels

Hi Maxime,

On Tue, Jul 20, 2021 at 7:15 PM Maxime Ripard <maxime@...no.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@...no.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.

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