linux-kernel - Re: [PATCH v5 8/8] drm/mediatek: Config orientation property if panel provides it

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Message-ID: <CAD=FV=Xe=iEh080QjE+Awgw0Q+Rb=xnrAj6OtO3EXp==XgvD0g@mail.gmail.com>
Date:   Tue, 7 Jun 2022 08:32:19 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthias Brugger <matthias.bgg@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Rob Clark <robdclark@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 8/8] drm/mediatek: Config orientation property if panel
 provides it

Hi,

On Tue, Jun 7, 2022 at 2:06 AM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
>
> Panel orientation property should be set before drm_dev_register().
> Mediatek drm driver calls drm_dev_register() in .bind(). However, most
> panels sets orientation property relatively late, mostly in .get_modes()
> callback, since this is when they are able to get the connector and
> binds the orientation property to it, though the value should be known
> when the panel is probed.
>
> Let the drm driver check if the remote end point is a panel and if it
> contains the orientation property. If it does, set it before
> drm_dev_register() is called.
>
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> Reviewed-by: Hans de Goede <hdegoede@...hat.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
> v4->v5:
> - use the new function in v5.
> - don't use drm_of_find_panel_or_bridge().
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index d9f10a33e6fa..998b1237e193 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -185,6 +185,7 @@ struct mtk_dsi {
>         struct drm_encoder encoder;
>         struct drm_bridge bridge;
>         struct drm_bridge *next_bridge;
> +       struct drm_panel *panel;
>         struct drm_connector *connector;
>         struct phy *phy;
>
> @@ -822,6 +823,10 @@ static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *dsi)
>                 ret = PTR_ERR(dsi->connector);
>                 goto err_cleanup_encoder;
>         }
> +
> +       /* Read panel orientation */
> +       drm_connector_set_orientation_from_panel(dsi->connector, dsi->panel);
> +
>         drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
>
>         return 0;
> @@ -836,6 +841,16 @@ static int mtk_dsi_bind(struct device *dev, struct device *master, void *data)
>         int ret;
>         struct drm_device *drm = data;
>         struct mtk_dsi *dsi = dev_get_drvdata(dev);
> +       struct device_node *panel_node;
> +
> +       /* Get panel if existed */
> +       panel_node = of_graph_get_remote_node(dev->of_node, 0, 0);
> +       if (panel_node) {
> +               dsi->panel = of_drm_find_panel(panel_node);
> +               if (IS_ERR(dsi->panel))
> +                       dsi->panel = NULL;
> +               of_node_put(panel_node);
> +       }

While the above works, it feels like we could do better. What about this?

* We add _some_ way to determine if a bridge is actually a
panel_bridge. If nothing else maybe this could be
drm_bridge_is_panel() and it could just check if bridge.funcs ==
panel_bridge_bridge_funcs

* In drm_bridge_connector_init(), when we're looping through all the
bridges we find the panel_bridge if it's there.

* At the end of drm_bridge_connector_init() if we found a panel_bridge
then we call a function like drm_panel_bridge_set_orientation().


Then you can fully get rid of the mediatek patch, right? The above
will only work if you're using a panel_bridge / bridge_connector, but
that's "the future" anyway and we want to encourage people to
transition to that.

-Doug