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

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Message-ID: <d6fe55b210888b9279c776b2bbfeaf38bfc44dcb@intel.com>
Date: Thu, 30 Oct 2025 11:44:11 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Ajye Huang <ajye_huang@...pal.corp-partner.google.com>,
 linux-kernel@...r.kernel.org
Cc: Douglas Anderson <dianders@...omium.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, Ajye Huang
 <ajye_huang@...pal.corp-partner.google.com>, jazhan@...gle.com
Subject: Re: [PATCH v1 1/2] drm/panel-edp: Add override bpc quirk for
 generic edp

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.

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