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

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Date:   Mon, 24 Oct 2022 15:22:21 -0400
From:   Hamza Mahfooz <hamza.mahfooz@....com>
To:     <linux-kernel@...r.kernel.org>
CC:     Roman Li <roman.li@....com>, Hamza Mahfooz <hamza.mahfooz@....com>,
        "Harry Wentland" <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        "Rodrigo Siqueira" <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        Fangzhi Zuo <Jerry.Zuo@....com>, Wayne Lin <Wayne.Lin@....com>,
        Lyude Paul <lyude@...hat.com>, Ian Chen <ian.chen@....com>,
        Claudio Suarez <cssk@...-c.es>,
        Colin Ian King <colin.king@...el.com>,
        hersen wu <hersenxs.wu@....com>,
        <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>
Subject: [PATCH 1/3] drm/edid: add a quirk for two LG monitors to get them to work on 10bpc

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@....com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
---
 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