RE: [PATCH v2 4/6] drm/edid: parse the DisplayID v2.0 VESA vendor block for MSO

On Mon, 13 Sep 2021, "Shankar, Uma" uma.shankar@intel.com wrote:

...

-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Jani Nikula Sent: Tuesday, August 31, 2021 7:48 PM To: intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org; ville.syrjala@linux.intel.com; Nikula, Jani jani.nikula@intel.com Subject: [PATCH v2 4/6] drm/edid: parse the DisplayID v2.0 VESA vendor block for MSO

The VESA Organization Vendor-Specific Data Block, defined in VESA DisplayID Standard v2.0, specifies the eDP Multi-SST Operation (MSO) stream count and segment pixel overlap.

DisplayID v1.3 has Appendix B: DisplayID as an EDID Extension, describing how DisplayID sections may be embedded in EDID extension blocks. DisplayID v2.0 does not have such a section, perhaps implying that DisplayID v2.0 data should not be included in EDID extensions, but rather in a "pure" DisplayID structure at its own DDC address pair A4h/A5h, as described in VESA E-DDC Standard v1.3 chapter 3.

However, in practice, displays out in the field have embedded DisplayID v2.0 data blocks in EDID extensions, including, in particular, some eDP MSO displays, where a pure DisplayID structure is not available at all.

Parse the MSO data from the DisplayID data block. Do it as part of drm_add_display_info(), extending it to parse also DisplayID data to avoid requiring extra calls to update the information.

v2: Check for VESA OUI (Ville)

Signed-off-by: Jani Nikula jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c | 72 +++++++++++++++++++++++++++++++++++++ include/drm/drm_connector.h | 12 +++++++ include/drm/drm_displayid.h | 13 +++++++ 3 files changed, 97 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 92974b1478bc..c45c225267ca 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -28,6 +28,7 @@

• DEALINGS IN THE SOFTWARE.

*/

+#include <linux/bitfield.h> #include <linux/hdmi.h> #include <linux/i2c.h> #include <linux/kernel.h> @@ -5145,6 +5146,71 @@ void drm_get_monitor_range(struct drm_connector *connector, info->monitor_range.max_vfreq); }

+static void drm_parse_vesa_mso_data(struct drm_connector *connector,

• 		    const struct displayid_block *block) {
  

• struct displayid_vesa_vendor_specific_block *vesa =

• (struct displayid_vesa_vendor_specific_block *)block;
  

• struct drm_display_info *info = &connector->display_info;
• if (block->num_bytes < 3) {

• drm_dbg_kms(connector->dev, "Unexpected vendor block size
  

%u\n",

• 	    block->num_bytes);
  

• return;
  

• }
• if (oui(vesa->oui[0], vesa->oui[1], vesa->oui[2]) != VESA_IEEE_OUI)

• return;
  

• if (sizeof(*vesa) != sizeof(*block) + block->num_bytes) {

• drm_dbg_kms(connector->dev, "Unexpected VESA vendor block
  

size\n");

• return;
  

• }
• switch (FIELD_GET(DISPLAYID_VESA_MSO_MODE, vesa->mso)) {
• default:

• drm_dbg_kms(connector->dev, "Reserved MSO mode value\n");
  

• fallthrough;
  

• case 0:

• info->mso_stream_count = 0;
  

• break;
  

• case 1:

• info->mso_stream_count = 2; /* 2 or 4 links */
  

• break;
  

• case 2:

• info->mso_stream_count = 4; /* 4 links */
  

• break;
  

• }
• if (!info->mso_stream_count) {

• info->mso_pixel_overlap = 0;
  

• return;
  

• }
• info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP,

vesa->mso);

• if (info->mso_pixel_overlap > 8) {

• drm_dbg_kms(connector->dev, "Reserved MSO pixel overlap value
  

%u\n",

• 	    info->mso_pixel_overlap);
  

• info->mso_pixel_overlap = 8;
  

Going beyond 8 is not right from a vendor perspective as it goes into reserved region. Should we not just set to 0 or how we decide that we fixed overlap at 8. It seems an undefined operation and it may vary from sink to sink.

I don't know if there's a right choice here. I don't mind setting it to 0 if you prefer that.

BR, Jani.

Regards, Uma Shankar

...

• }
• drm_dbg_kms(connector->dev, "MSO stream count %u, pixel overlap %u\n",

•     info->mso_stream_count, info->mso_pixel_overlap); }
  

+static void drm_update_mso(struct drm_connector *connector, const +struct edid *edid) {

• const struct displayid_block *block;
• struct displayid_iter iter;
• displayid_iter_edid_begin(edid, &iter);
• displayid_iter_for_each(block, &iter) {

• if (block->tag == DATA_BLOCK_2_VENDOR_SPECIFIC)
  

• 	drm_parse_vesa_mso_data(connector, block);
  

• }
• displayid_iter_end(&iter);

+}

/* A connector has no EDID information, so we've got no EDID to compute quirks from. Reset

• all of the values which would have been set from EDID

*/ @@ -5168,6 +5234,9 @@ drm_reset_display_info(struct drm_connector *connector)

info->non_desktop = 0; memset(&info->monitor_range, 0, sizeof(info->monitor_range));

• info->mso_stream_count = 0;
• info->mso_pixel_overlap = 0;

}

u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edid) @@ -5246,6 +5315,9 @@ u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edi info->color_formats |= DRM_COLOR_FORMAT_YCRCB444; if (edid->features & DRM_EDID_FEATURE_RGB_YCRCB422) info->color_formats |= DRM_COLOR_FORMAT_YCRCB422;

• drm_update_mso(connector, edid);
• return quirks;

}

diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h index 79fa34e5ccdb..379746d3266f 100644 --- a/include/drm/drm_connector.h +++ b/include/drm/drm_connector.h @@ -590,6 +590,18 @@ struct drm_display_info { * @monitor_range: Frequency range supported by monitor range descriptor */ struct drm_monitor_range_info monitor_range;

• /**

• * @mso_stream_count: eDP Multi-SST Operation (MSO) stream count from
  

• * the DisplayID VESA vendor block. 0 for conventional Single-Stream
  

• * Transport (SST), or 2 or 4 MSO streams.
  

• */
  

• u8 mso_stream_count;
• /**

• * @mso_pixel_overlap: eDP MSO segment pixel overlap, 0-8 pixels.
  

• */
  

• u8 mso_pixel_overlap;

};

int drm_display_info_set_bus_formats(struct drm_display_info *info, diff --git a/include/drm/drm_displayid.h b/include/drm/drm_displayid.h index 79771091771a..7ffbd9f7bfc7 100644 --- a/include/drm/drm_displayid.h +++ b/include/drm/drm_displayid.h @@ -23,9 +23,12 @@ #define DRM_DISPLAYID_H

#include <linux/types.h> +#include <linux/bits.h>

struct edid;

+#define VESA_IEEE_OUI 0x3a0292

/* DisplayID Structure versions */ #define DISPLAY_ID_STRUCTURE_VER_12 0x12 #define DISPLAY_ID_STRUCTURE_VER_20 0x20 @@ -126,6 +129,16 @@ struct displayid_detailed_timing_block { struct displayid_detailed_timings_1 timings[]; };

+#define DISPLAYID_VESA_MSO_OVERLAP GENMASK(3, 0) +#define DISPLAYID_VESA_MSO_MODE GENMASK(6, 5)

+struct displayid_vesa_vendor_specific_block {

• struct displayid_block base;
• u8 oui[3];
• u8 data_structure_type;
• u8 mso;

+} __packed;

/* DisplayID iteration */ struct displayid_iter { const struct edid *edid; -- 2.30.2