Re: [PATCH v3 2/3] drm/edid: parse panel type from DisplayID 2.x Display Parameters

["Chen, Chen-Yu" <Chen-Yu.Chen@amd.com>]

I forgot to include Mario's Reviewed-by in the commit message:

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>

On 5/26/2026 10:59 AM, Chenyu Chen wrote:
> Parse the Display Parameters Data Block (tag 0x21) defined in
> DisplayID v2.1a Section 4.2.6. Extract the Display Device Technology
> field from the color depth and device technology byte, which indicates
> whether the panel uses LCD or OLED technology.
> 
> Add a panel_type field to struct drm_display_info and populate it
> during DisplayID iteration so downstream drivers can use it for
> panel-type-dependent behavior. Add DRM_MODE_PANEL_TYPE_LCD to the UAPI
> panel type property alongside the existing OLED value.
> 
> Assisted-by: Copilot:Claude-Opus-4.6
> Signed-off-by: Chenyu Chen <chen-yu.chen@amd.com>
> ---
>  drivers/gpu/drm/drm_connector.c          |  3 +-
>  drivers/gpu/drm/drm_displayid_internal.h | 24 +++++++++++++
>  drivers/gpu/drm/drm_edid.c               | 45 ++++++++++++++++++++++++
>  include/drm/drm_connector.h              |  6 ++++
>  include/uapi/drm/drm_mode.h              |  1 +
>  5 files changed, 78 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index aec05adbc889..f2ac4542a7d3 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -1176,6 +1176,7 @@ static const struct drm_prop_enum_list drm_link_status_enum_list[] = {
>  static const struct drm_prop_enum_list drm_panel_type_enum_list[] = {
>  	{ DRM_MODE_PANEL_TYPE_UNKNOWN, "unknown" },
>  	{ DRM_MODE_PANEL_TYPE_OLED, "OLED" },
> +	{ DRM_MODE_PANEL_TYPE_LCD, "LCD" },
>  };
>  
>  /**
> @@ -1508,7 +1509,7 @@ EXPORT_SYMBOL(drm_hdmi_connector_get_output_format_name);
>   * 	never read back the value of "DPMS" because it can be incorrect.
>   * panel_type:
>   * 	Immutable enum property to indicate the type of connected panel.
> - * 	Possible values are "unknown" (default) and "OLED".
> + * 	Possible values are "unknown" (default), "OLED", and "LCD".
>   * PATH:
>   * 	Connector path property to identify how this sink is physically
>   * 	connected. Used by DP MST. This should be set by calling
> diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
> index 5b1b32f73516..6f431aafafcf 100644
> --- a/drivers/gpu/drm/drm_displayid_internal.h
> +++ b/drivers/gpu/drm/drm_displayid_internal.h
> @@ -142,6 +142,30 @@ struct displayid_formula_timing_block {
>  	struct displayid_formula_timings_9 timings[];
>  } __packed;
>  
> +#define DISPLAYID_DEVICE_TECH_UNSPECIFIED	0
> +#define DISPLAYID_DEVICE_TECH_LCD		1
> +#define DISPLAYID_DEVICE_TECH_OLED		2
> +
> +#define DISPLAYID_DISPLAY_PARAMS_DEVICE_TECH	GENMASK(6, 4)
> +
> +struct displayid_display_params_block {
> +	struct displayid_block base;
> +	__le16 horiz_image_size;
> +	__le16 vert_image_size;
> +	__le16 horiz_pixel_count;
> +	__le16 vert_pixel_count;
> +	u8 features;
> +	u8 primary_color1[3];
> +	u8 primary_color2[3];
> +	u8 primary_color3[3];
> +	u8 white_point[3];
> +	__le16 max_luminance_full;
> +	__le16 max_luminance_10;
> +	__le16 min_luminance;
> +	u8 color_depth_and_tech;	/* [2:0] depth, [6:4] device tech, [7] theme */
> +	u8 gamma_eotf;
> +} __packed;
> +
>  #define DISPLAYID_VESA_MSO_OVERLAP	GENMASK(3, 0)
>  #define DISPLAYID_VESA_MSO_MODE		GENMASK(6, 5)
>  
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 7ad3f939dbe6..a9d480981c8f 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -6713,6 +6713,8 @@ static void drm_reset_display_info(struct drm_connector *connector)
>  
>  	info->source_physical_address = CEC_PHYS_ADDR_INVALID;
>  	memset(&info->amd_vsdb, 0, sizeof(info->amd_vsdb));
> +
> +	info->panel_type = DRM_MODE_PANEL_TYPE_UNKNOWN;
>  }
>  
>  static void drm_displayid_process_base_section_header(struct drm_connector *connector,
> @@ -6731,6 +6733,45 @@ static void drm_displayid_process_base_section_header(struct drm_connector *conn
>  		info->non_desktop = true;
>  }
>  
> +static void
> +drm_displayid_parse_display_params(struct drm_connector *connector,
> +				   const struct displayid_block *block)
> +{
> +	struct drm_display_info *info = &connector->display_info;
> +	const struct displayid_display_params_block *params =
> +		(const struct displayid_display_params_block *)block;
> +	u8 tech;
> +
> +	if (block->num_bytes < sizeof(*params) - sizeof(params->base)) {
> +		drm_dbg_kms(connector->dev,
> +			    "[CONNECTOR:%d:%s] DisplayID Display Parameters block too short (%u < %zu)\n",
> +			    connector->base.id, connector->name,
> +			    block->num_bytes,
> +			    sizeof(*params) - sizeof(params->base));
> +		return;
> +	}
> +
> +	tech = FIELD_GET(DISPLAYID_DISPLAY_PARAMS_DEVICE_TECH,
> +			 params->color_depth_and_tech);
> +
> +	drm_dbg_kms(connector->dev,
> +		    "[CONNECTOR:%d:%s] DisplayID Display Parameters: device technology %s\n",
> +		    connector->base.id, connector->name,
> +		    tech == DISPLAYID_DEVICE_TECH_LCD ? "LCD" :
> +		    tech == DISPLAYID_DEVICE_TECH_OLED ? "OLED" : "unspecified");
> +
> +	switch (tech) {
> +	case DISPLAYID_DEVICE_TECH_LCD:
> +		info->panel_type = DRM_MODE_PANEL_TYPE_LCD;
> +		break;
> +	case DISPLAYID_DEVICE_TECH_OLED:
> +		info->panel_type = DRM_MODE_PANEL_TYPE_OLED;
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
>  static void update_displayid_info(struct drm_connector *connector,
>  				  const struct drm_edid *drm_edid)
>  {
> @@ -6744,6 +6785,10 @@ static void update_displayid_info(struct drm_connector *connector,
>  			drm_displayid_process_base_section_header(connector, &iter);
>  			base_section_header_processed = true;
>  		}
> +
> +		if (displayid_version(&iter) == DISPLAY_ID_STRUCTURE_VER_20 &&
> +		    block->tag == DATA_BLOCK_2_DISPLAY_PARAMETERS)
> +			drm_displayid_parse_display_params(connector, block);
>  	}
>  	displayid_iter_end(&iter);
>  }
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index c398dbc68bbc..745cd917fe40 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -899,6 +899,12 @@ struct drm_display_info {
>  	 * @amd_vsdb: AMD-specific VSDB information.
>  	 */
>  	struct drm_amd_vsdb_info amd_vsdb;
> +
> +	/**
> +	 * @panel_type: Panel type from DisplayID Display Parameters
> +	 * Data Block (tag 0x21). Uses DRM_MODE_PANEL_TYPE_* constants.
> +	 */
> +	u8 panel_type;
>  };
>  
>  int drm_display_info_set_bus_formats(struct drm_display_info *info,
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index 3693d82b5279..d7ca1040b92e 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -169,6 +169,7 @@ extern "C" {
>  /* Panel type property */
>  #define DRM_MODE_PANEL_TYPE_UNKNOWN	0
>  #define DRM_MODE_PANEL_TYPE_OLED	1
> +#define DRM_MODE_PANEL_TYPE_LCD		2
>  
>  /*
>   * DRM_MODE_ROTATE_<degrees>