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

[Leo Li <sunpeng.li@amd.com>]

On 2026-05-15 04:23, Jani Nikula wrote:
> 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?
> 

I think the intention is to log and process the DisplayID base section header only once instead on every
iteration. Maybe a `bool header_processed` works better?

- Leo

>> +
>>  		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>
>