[PATCH 3/5] drm/edid: parse the DisplayID v2.0 VESA vendor block for MSO

[Jani Nikula]

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.

Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/drm_edid.c  | 63 +++++++++++++++++++++++++++++++++++++
 include/drm/drm_connector.h | 12 +++++++
 include/drm/drm_displayid.h | 11 +++++++
 3 files changed, 86 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 6325877c5fd6..7e8083068f3f 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>
@@ -5148,6 +5149,62 @@ 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 (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;
+	}
+
+	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
  */
@@ -5171,6 +5228,9 @@ 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)
@@ -5249,6 +5309,9 @@ 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..b18611e016a2 100644
--- a/include/drm/drm_displayid.h
+++ b/include/drm/drm_displayid.h
@@ -23,6 +23,7 @@
 #define DRM_DISPLAYID_H
 
 #include <linux/types.h>
+#include <linux/bits.h>
 
 struct edid;
 
@@ -126,6 +127,16 @@ 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;
-- 
2.20.1