[PATCH 1/3] drm/edid: add a quirk for two LG monitors to get them to work on 10bpc

[Hamza Mahfooz <hamza.mahfooz@xxxxxxx>]

The LG 27GP950 and LG 27GN950 have visible display corruption when
trying to use 10bpc modes. So, to fix this, cap their maximum DSC
target bitrate to 15bpp.

Suggested-by: Roman Li <roman.li@xxxxxxx>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@xxxxxxx>
---
 drivers/gpu/drm/drm_edid.c  | 12 ++++++++++++
 include/drm/drm_connector.h |  6 ++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index bc43e1b32092..f4f96115dce7 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -91,6 +91,8 @@ static int oui(u8 first, u8 second, u8 third)
 #define EDID_QUIRK_FORCE_10BPC			(1 << 11)
 /* Non desktop display (i.e. HMD) */
 #define EDID_QUIRK_NON_DESKTOP			(1 << 12)
+/* Cap the DSC target bitrate to 15bpp */
+#define EDID_QUIRK_CAP_DSC_15BPP		(1 << 13)
 
 #define MICROSOFT_IEEE_OUI	0xca125c
 
@@ -151,6 +153,12 @@ static const struct edid_quirk {
 	EDID_QUIRK('F', 'C', 'M', 13600, EDID_QUIRK_PREFER_LARGE_75 |
 				       EDID_QUIRK_DETAILED_IN_CM),
 
+	/* LG 27GP950 */
+	EDID_QUIRK('G', 'S', 'M', 0x5bbf, EDID_QUIRK_CAP_DSC_15BPP),
+
+	/* LG 27GN950 */
+	EDID_QUIRK('G', 'S', 'M', 0x5b9a, EDID_QUIRK_CAP_DSC_15BPP),
+
 	/* LGD panel of HP zBook 17 G2, eDP 10 bpc, but reports unknown bpc */
 	EDID_QUIRK('L', 'G', 'D', 764, EDID_QUIRK_FORCE_10BPC),
 
@@ -5511,6 +5519,7 @@ drm_reset_display_info(struct drm_connector *connector)
 
 	info->mso_stream_count = 0;
 	info->mso_pixel_overlap = 0;
+	info->max_dsc_bpp = 0;
 }
 
 u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edid)
@@ -5595,6 +5604,9 @@ u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edi
 		info->non_desktop = true;
 	}
 
+	if (quirks & EDID_QUIRK_CAP_DSC_15BPP)
+		info->max_dsc_bpp = 15;
+
 	return quirks;
 }
 
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 3ac4bf87f257..7a8fb486b6ab 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -634,6 +634,12 @@ struct drm_display_info {
 	 * @mso_pixel_overlap: eDP MSO segment pixel overlap, 0-8 pixels.
 	 */
 	u8 mso_pixel_overlap;
+
+	/**
+	 * @max_dsc_bpp: Maximum DSC target bitrate, if it is set to 0 the
+	 * monitor's default value is used instead.
+	 */
+	u32 max_dsc_bpp;
 };
 
 int drm_display_info_set_bus_formats(struct drm_display_info *info,
-- 
2.38.0