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

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Date:   Wed, 8 Jun 2022 17:35:27 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Doug Anderson <dianders@...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

On Tue, Jun 7, 2022 at 11:39 PM Doug Anderson <dianders@...omium.org> wrote:
>
> 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.
>
This also works with the mtk dsi, and it's more generic. I'll drop
this patch and go with this implementation in the next version. Thanks
for the suggestion.

> -Doug