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

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

On 5/16/2026 7:47 AM, Leo Li wrote:
> 
> 
> 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
> 

The intention was to keep section-level drm_dbg_kms logging for better debugging visibility.

That said, I agree that this does not belong in the iterator directly and should be refactored into a helper.

>>> +
>>>  		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.
>>
>>

You're right, the current patches are hard to follow due to mixing refactoring and new logic.

I will refactor the code into helper functions and split the changes into smaller patches, then resend the updated series.

Thanks for the suggestions.

Regards,
Chenyu

>>>  	}
>>>  	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>
>>
>