On 2026-05-15 04:23, Jani Nikula wrote:
> On Thu, 14 May 2026, Chenyu Chen <[email protected]> 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 <[email protected]>
>> Reviewed-by: Mario Limonciello <[email protected]>
>> ---
>> 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>
>
