linux-kernel - Re: [PATCH v1 1/2] drm/panel-edp: Add override bpc quirk for generic edp

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Message-ID: <CAD=FV=UTP-kdjp2DD0YYnwmQ7ppLKXSHLRybPbyPeSqE_FEQMA@mail.gmail.com>
Date: Thu, 30 Oct 2025 08:10:15 -0700
From: Doug Anderson <dianders@...omium.org>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Ajye Huang <ajye_huang@...pal.corp-partner.google.com>, linux-kernel@...r.kernel.org, 
	Neil Armstrong <neil.armstrong@...aro.org>, Jessica Zhang <jesszhan0024@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	dri-devel@...ts.freedesktop.org, jazhan@...gle.com
Subject: Re: [PATCH v1 1/2] drm/panel-edp: Add override bpc quirk for generic edp

Hi,

On Thu, Oct 30, 2025 at 2:44 AM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
>
> On Wed, 29 Oct 2025, Ajye Huang <ajye_huang@...pal.corp-partner.google.com> wrote:
> > Adding override bpc to EDP_PANEL_ENTRY3 quirk.
> >
> > Signed-off-by: Ajye Huang <ajye_huang@...pal.corp-partner.google.com>
> > ---
> >  drivers/gpu/drm/panel/panel-edp.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
> > index 944c7c70de55..da3e8f223ec3 100644
> > --- a/drivers/gpu/drm/panel/panel-edp.c
> > +++ b/drivers/gpu/drm/panel/panel-edp.c
> > @@ -218,6 +218,9 @@ struct edp_panel_entry {
> >
> >       /** @override_edid_mode: Override the mode obtained by edid. */
> >       const struct drm_display_mode *override_edid_mode;
> > +
> > +     /** @override_bpc: Override the Bits per color obtained by edid. */
> > +     unsigned int override_bpc;
> >  };
> >
> >  struct panel_edp {
> > @@ -586,6 +589,9 @@ static int panel_edp_get_modes(struct drm_panel *panel,
> >       bool has_override_edid_mode = p->detected_panel &&
> >                                     p->detected_panel != ERR_PTR(-EINVAL) &&
> >                                     p->detected_panel->override_edid_mode;
>
> Unrelated to the patch at hand, since the pattern is there already, but
> something like this should be more reliable:
>
> bool has_override_edid_mode = !IS_ERR_OR_NULL(p->detected_panel) &&
>         p->detected_panel->override_edid_mode;
>
> It does not look like p->detected_panel could have other error pointer
> values than -EINVAL, but it looks awkward to check for NULL and one
> error pointer value, and then go on to dereference it.
>
> I guess even better would be to always use either NULL *or* error
> pointers, not a mix, but I digress.

Yeah, that makes sense. If someone wants to send a patch cleaning this
up, I'd be happy to review it! :-)

-Doug