linux-kernel - Re: [PATCH 2/2] drm/bridge: parade-ps8640: Populate devices on aux-bus

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Date:   Mon, 18 Oct 2021 13:43:46 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Philip Chen <philipchen@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 2/2] drm/bridge: parade-ps8640: Populate devices on aux-bus

Hi,

On Sat, Oct 16, 2021 at 9:57 AM Philip Chen <philipchen@...omium.org> wrote:
>
> Conventionally, panel is listed under the root in the device tree.
> When userland asks for display mode, ps8640 bridge is responsible
> for returning EDID when ps8640_bridge_get_edid() is called.
>
> Now enable a new option of listing the panel under "aux-bus" of ps8640
> bridge node in the device tree. In this case, panel driver can retrieve
> EDID by triggering AUX transactions, without ps8640_bridge_get_edid()
> calls at all.
>
> To prevent the "old" and "new" options from interfering with each
> other's logic flow, disable DRM_BRIDGE_OP_EDID when the new option
> is taken.
>
> Signed-off-by: Philip Chen <philipchen@...omium.org>
> ---
>
>  drivers/gpu/drm/bridge/parade-ps8640.c | 52 ++++++++++++++++++++------
>  1 file changed, 40 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> index acfe1bf0f936..98884f799ea8 100644
> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> @@ -14,6 +14,7 @@
>  #include <linux/regulator/consumer.h>
>
>  #include <drm/drm_bridge.h>
> +#include <drm/drm_dp_aux_bus.h>

You need a `select DRM_DP_AUX_BUS` in the Kconfig to avoid the errors
that the build robot found for you.


>  #include <drm/drm_dp_helper.h>
>  #include <drm/drm_mipi_dsi.h>
>  #include <drm/drm_of.h>
> @@ -149,6 +150,24 @@ static inline struct ps8640 *aux_to_ps8640(struct drm_dp_aux *aux)
>         return container_of(aux, struct ps8640, aux);
>  }
>
> +static bool ps8640_of_panel_on_aux_bus(struct device *dev)
> +{
> +       struct device_node *bus, *panel;
> +
> +       if (!dev->of_node)
> +               return false;

You probably don't need the above check. I think things would be
pretty broken if we didn't have an "of_node".


> +       bus = of_get_child_by_name(dev->of_node, "aux-bus");
> +       if (!bus)
> +               return false;
> +
> +       panel = of_get_child_by_name(bus, "panel");

of_node_put(bus);


> +       if (!panel)
> +               return false;

of_node_put(panel);


Other than the above, this looks reasonable to me.

-Doug