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

From: Philip Chen <philipchen@chromium.org>
To: Doug Anderson <dianders@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Robert Foss <robert.foss@linaro.org>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 2/2] drm/bridge: parade-ps8640: Populate devices on aux-bus
Date: Thu, 21 Oct 2021 14:11:19 -0700	[thread overview]
Message-ID: <CA+cxXh=R3U2uz2x0Mef3LZ-mta-+F9TXD0F+RGd5mDTWQOgZvQ@mail.gmail.com> (raw)
In-Reply-To: <CAD=FV=XXOY_Rded_j6oysDkZ=e7_Gc1SPKPbkLK2DBdoKHWuKA@mail.gmail.com>

Hi Doug,

On Mon, Oct 18, 2021 at 1:43 PM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Sat, Oct 16, 2021 at 9:57 AM Philip Chen <philipchen@chromium.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@chromium.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.
Thanks for the tip!
I also found "select REGMAP_I2C" seems to be missing for ps8640.
although the build robot didn't complain.
Should I post a fix-up?

>
>
> >  #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".
Removed in v2.
PTAL.
>
>
> > +       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);
Added in v2.
PTAL.

>
>
> > +       if (!panel)
> > +               return false;
>
> of_node_put(panel);
Added in v2.
PTAL.
>
>
> Other than the above, this looks reasonable to me.
>
> -Doug