Re: [PATCH 1/2] drm/edid: parse panel type from DisplayID 2.x Display Parameters block

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 14 May 2026, Chenyu Chen <chen-yu.chen@amd.com> 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 payload byte 27, bits [6:4], which indicates whether the
> panel is LCD (001b) or OLED (010b).
>
> Store the result in drm_display_info.did_panel_type so that downstream
> drivers can use it for panel-type-dependent behavior.
>
> Assisted-by: Copilot:Claude-Opus-4.6
> Signed-off-by: Chenyu Chen <chen-yu.chen@amd.com>
> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  drivers/gpu/drm/drm_displayid_internal.h | 25 ++++++++++
>  drivers/gpu/drm/drm_edid.c               | 61 +++++++++++++++++++-----
>  include/drm/drm_connector.h              |  6 +++
>  include/uapi/drm/drm_mode.h              |  1 +
>  4 files changed, 82 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
> index 5b1b32f73516..e0f7c54d2987 100644
> --- a/drivers/gpu/drm/drm_displayid_internal.h
> +++ b/drivers/gpu/drm/drm_displayid_internal.h
> @@ -142,6 +142,31 @@ struct displayid_formula_timing_block {
>  	struct displayid_formula_timings_9 timings[];
>  } __packed;
>  
> +/*
> + * DisplayID v2.x Display Parameters Data Block (tag 0x21).
> + *
> + * Per VESA DisplayID v2.1a, Section 4.2.6, Table 4-14:
> + * Offset 0x1E (payload byte 27) contains Native Color Depth and
> + * Display Device Technology fields.
> + *   bits [2:0] = Native Color Depth
> + *   bit  [3]   = RESERVED
> + *   bits [6:4] = Display Device Technology
> + *     000b = not specified, 001b = LCD, 010b = OLED, others reserved
> + *   bit  [7]   = Display Device Theme Preference
> + */
> +#define DISPLAYID_DISPLAY_PARAMS_DEVICE_TECH	GENMASK(6, 4)
> +
> +struct displayid_display_params_block {
> +	struct displayid_block base;
> +	u8 payload[27];
> +	u8 device_tech_byte; /* bits [6:4] = Display Device Technology */
> +	u8 reserved;
> +} __packed;
> +
> +#define DISPLAYID_DISPLAY_PARAMS_MIN_LEN	\
> +	(sizeof(struct displayid_display_params_block) -	\
> +	 sizeof(struct displayid_block))
> +
>  #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 8031f021d4d0..9b160a878df4 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->did_panel_type = DRM_MODE_PANEL_TYPE_UNKNOWN;
>  }
>  
>  static void update_displayid_info(struct drm_connector *connector,
> @@ -6721,24 +6723,61 @@ static void update_displayid_info(struct drm_connector *connector,
>  	struct drm_display_info *info = &connector->display_info;
>  	const struct displayid_block *block;
>  	struct displayid_iter iter;
> +	const u8 *section = NULL;
>  
>  	displayid_iter_edid_begin(drm_edid, &iter);
>  	displayid_iter_for_each(block, &iter) {
> +		if (section != iter.section) {
> +			drm_dbg_kms(connector->dev,
> +				    "[CONNECTOR:%d:%s] DisplayID extension version 0x%02x, primary use 0x%02x\n",
> +				    connector->base.id, connector->name,
> +				    displayid_version(&iter),
> +				    displayid_primary_use(&iter));
> +			if (displayid_version(&iter) == DISPLAY_ID_STRUCTURE_VER_20 &&
> +			    (displayid_primary_use(&iter) == PRIMARY_USE_HEAD_MOUNTED_VR ||
> +			     displayid_primary_use(&iter) == PRIMARY_USE_HEAD_MOUNTED_AR))
> +				info->non_desktop = true;
> +			section = iter.section;
> +		}

What is this even supposed to do?

> +
>  		drm_dbg_kms(connector->dev,
> -			    "[CONNECTOR:%d:%s] DisplayID extension version 0x%02x, primary use 0x%02x\n",
> +			    "[CONNECTOR:%d:%s] DisplayID block tag 0x%02x, rev 0x%02x, size %u\n",
>  			    connector->base.id, connector->name,
> -			    displayid_version(&iter),
> -			    displayid_primary_use(&iter));
> +			    block->tag, block->rev, block->num_bytes);
> +
>  		if (displayid_version(&iter) == DISPLAY_ID_STRUCTURE_VER_20 &&
> -		    (displayid_primary_use(&iter) == PRIMARY_USE_HEAD_MOUNTED_VR ||
> -		     displayid_primary_use(&iter) == PRIMARY_USE_HEAD_MOUNTED_AR))
> -			info->non_desktop = true;
> +		    block->tag == DATA_BLOCK_2_DISPLAY_PARAMETERS) {
> +			const struct displayid_display_params_block *params =
> +				(const struct displayid_display_params_block *)block;
> +			u8 tech;
> +
> +			if (block->num_bytes < DISPLAYID_DISPLAY_PARAMS_MIN_LEN) {
> +				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,
> +					    DISPLAYID_DISPLAY_PARAMS_MIN_LEN);
> +				continue;
> +			}
>  
> -		/*
> -		 * We're only interested in the base section here, no need to
> -		 * iterate further.
> -		 */
> -		break;
> +			tech = FIELD_GET(DISPLAYID_DISPLAY_PARAMS_DEVICE_TECH,
> +					 params->device_tech_byte);
> +
> +			drm_dbg_kms(connector->dev,
> +				    "[CONNECTOR:%d:%s] DisplayID Display Parameters: device technology %u\n",
> +				    connector->base.id, connector->name, tech);
> +
> +			switch (tech) {
> +			case 1: /* LCD */
> +				info->did_panel_type = DRM_MODE_PANEL_TYPE_LCD;
> +				break;
> +			case 2: /* OLED */
> +				info->did_panel_type = DRM_MODE_PANEL_TYPE_OLED;
> +				break;
> +			default:
> +				break;
> +			}
> +		}

Please tell copilot to not add so much crap in the iterator block. Add
functions. Add the first function as a refactor for non_desktop, add
more stuff on top, i.e. split this into multiple patches.

BR,
Jani.


>  	}
>  	displayid_iter_end(&iter);
>  }
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index c398dbc68bbc..b95aec34ddb7 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;
> +
> +	/**
> +	 * @did_panel_type: Panel type from DisplayID Display Parameters
> +	 * Data Block (tag 0x21). Uses DRM_MODE_PANEL_TYPE_* constants.
> +	 */
> +	u8 did_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>

-- 
Jani Nikula, Intel