Add EDP_PANEL_ENTRY3 to override bpc

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

Posted by Ajye Huang 1 month, 2 weeks ago

Adding override bpc to EDP_PANEL_ENTRY3 quirk.

Signed-off-by: Ajye Huang <ajye_huang@compal.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;
+	bool has_override_bpc = p->detected_panel &&
+				      p->detected_panel != ERR_PTR(-EINVAL) &&
+				      p->detected_panel->override_bpc;
 
 	/* probe EDID if a DDC bus is available */
 	if (p->ddc) {
@@ -611,6 +617,9 @@ static int panel_edp_get_modes(struct drm_panel *panel,
 			} else {
 				num += drm_edid_connector_add_modes(connector);
 			}
+
+			if (has_override_bpc)
+				connector->display_info.bpc = p->detected_panel->override_bpc;
 		}
 
 		pm_runtime_mark_last_busy(panel->dev);
@@ -1871,6 +1880,17 @@ static const struct panel_delay delay_80_500_e50_d50 = {
 	.override_edid_mode = _mode \
 }
 
+#define EDP_PANEL_ENTRY3(vend_chr_0, vend_chr_1, vend_chr_2, product_id, _delay, _name, _bpc) \
+{ \
+	.ident = { \
+		.name = _name, \
+		.panel_id = drm_edid_encode_panel_id(vend_chr_0, vend_chr_1, vend_chr_2, \
+						     product_id), \
+	}, \
+	.delay = _delay, \
+	.override_bpc = _bpc \
+}
+
 /*
  * This table is used to figure out power sequencing delays for panels that
  * are detected by EDID. Entries here may point to entries in the
-- 
2.25.1

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

Posted by Jani Nikula 1 month, 2 weeks ago

On Wed, 29 Oct 2025, Ajye Huang <ajye_huang@compal.corp-partner.google.com> wrote:
> Adding override bpc to EDP_PANEL_ENTRY3 quirk.
>
> Signed-off-by: Ajye Huang <ajye_huang@compal.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.

BR,
Jani.


> +	bool has_override_bpc = p->detected_panel &&
> +				      p->detected_panel != ERR_PTR(-EINVAL) &&
> +				      p->detected_panel->override_bpc;
>  
>  	/* probe EDID if a DDC bus is available */
>  	if (p->ddc) {
> @@ -611,6 +617,9 @@ static int panel_edp_get_modes(struct drm_panel *panel,
>  			} else {
>  				num += drm_edid_connector_add_modes(connector);
>  			}
> +
> +			if (has_override_bpc)
> +				connector->display_info.bpc = p->detected_panel->override_bpc;
>  		}
>  
>  		pm_runtime_mark_last_busy(panel->dev);
> @@ -1871,6 +1880,17 @@ static const struct panel_delay delay_80_500_e50_d50 = {
>  	.override_edid_mode = _mode \
>  }
>  
> +#define EDP_PANEL_ENTRY3(vend_chr_0, vend_chr_1, vend_chr_2, product_id, _delay, _name, _bpc) \
> +{ \
> +	.ident = { \
> +		.name = _name, \
> +		.panel_id = drm_edid_encode_panel_id(vend_chr_0, vend_chr_1, vend_chr_2, \
> +						     product_id), \
> +	}, \
> +	.delay = _delay, \
> +	.override_bpc = _bpc \
> +}
> +
>  /*
>   * This table is used to figure out power sequencing delays for panels that
>   * are detected by EDID. Entries here may point to entries in the

-- 
Jani Nikula, Intel

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

Posted by Doug Anderson 1 month, 2 weeks ago

Hi,

On Thu, Oct 30, 2025 at 2:44 AM Jani Nikula <jani.nikula@linux.intel.com> wrote:
>
> On Wed, 29 Oct 2025, Ajye Huang <ajye_huang@compal.corp-partner.google.com> wrote:
> > Adding override bpc to EDP_PANEL_ENTRY3 quirk.
> >
> > Signed-off-by: Ajye Huang <ajye_huang@compal.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

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

Posted by Doug Anderson 1 month, 2 weeks ago

Hi,

On Wed, Oct 29, 2025 at 1:11 AM Ajye Huang
<ajye_huang@compal.corp-partner.google.com> wrote:
>
> Adding override bpc to EDP_PANEL_ENTRY3 quirk.
>
> Signed-off-by: Ajye Huang <ajye_huang@compal.corp-partner.google.com>
> ---
>  drivers/gpu/drm/panel/panel-edp.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)

This seems OK to me. I'd be OK with:

Reviewed-by: Douglas Anderson <dianders@chromium.org>

I think you could alternatively add a EDID_QUIRK_FORCE_6BPC quirk for
this panel in "drivers/gpu/drm/drm_edid.c", though I haven't tested
it. That _might_ be a better solution? Maybe Jani or someone else CCed
would have an opinion.

At first I was thinking that the quirks in "drm_edid.c" were probably
just for "DP" display, but then I just realized that they probably
also are for "eDP" panels. Specifically I think Intel hardware doesn't
use panel-edp.c so I think the only place quirks could get applied (if
an eDP panel was also used on Intel hardware) was from "drm_edid.c".

Any chance you could confirm if EDID_QUIRK_FORCE_6BPC works for you?

Does anyone else CCed have an opinion of which they like better?

-Doug

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

Posted by Jani Nikula 1 month, 2 weeks ago

On Wed, 29 Oct 2025, Doug Anderson <dianders@chromium.org> wrote:
> At first I was thinking that the quirks in "drm_edid.c" were probably
> just for "DP" display, but then I just realized that they probably
> also are for "eDP" panels. Specifically I think Intel hardware doesn't
> use panel-edp.c so I think the only place quirks could get applied (if
> an eDP panel was also used on Intel hardware) was from "drm_edid.c".
>
> Any chance you could confirm if EDID_QUIRK_FORCE_6BPC works for you?
>
> Does anyone else CCed have an opinion of which they like better?

No strong opinions, but obviously having it in drm_edid.c would be more
generic. Until you encounter panels where you need to force something
other than 6 bpc, when it stops being generic and becomes an
obstacle. ;)

BR,
Jani.

-- 
Jani Nikula, Intel

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

Posted by Ajye Huang 1 month, 2 weeks ago

Hi Doug,

On Thu, Oct 30, 2025 at 7:21 AM Doug Anderson <dianders@chromium.org> wrote:

> At first I was thinking that the quirks in "drm_edid.c" were probably
> just for "DP" display, but then I just realized that they probably
> also are for "eDP" panels. Specifically I think Intel hardware doesn't
> use panel-edp.c so I think the only place quirks could get applied (if
> an eDP panel was also used on Intel hardware) was from "drm_edid.c".
>
> Any chance you could confirm if EDID_QUIRK_FORCE_6BPC works for you?

The following quirks added in drm_edid.c is workable,
+       /* Sharp LQ116M1JW10 reports 8 bpc and it  will display noise,
but display noiseless as 6 bpc  */
+       EDID_QUIRK('S', 'H', 'P', 0x154c, EDID_QUIRK_FORCE_6BPC),

I will send upstream a new patch for modifying the drm_edid.c , thank
you so much