[PATCH 1/1] drm: This patch fixes colour banding caused by wrong information passed by the Lenovo Thinkpad L540 panel.

From: Francesco Paolo Lovergine <frankie@debian.org>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Subject: [PATCH 1/1] drm: This patch fixes colour banding caused by wrong information passed by the Lenovo Thinkpad L540 panel.
Date: Thu, 23 Sep 2021 13:10:46 +0200	[thread overview]
Message-ID: <YUhseVXMsTJKAqF6@legolas.home.lovergine.com> (raw)

Hi, 

there is an issue with Lenovo Thinkpad L540 very similar to those described here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1749420 or here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1788308
that is a bad looking color banding with dark colors mainly.
It happens with any kernel starting from 4.8 up to the current.

Signed-off-by: Francesco Paolo Lovergine <frankie@debian.org>
---
 drivers/gpu/drm/drm_edid.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 6325877c5fd6..48e06cc33e4d 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -141,6 +141,9 @@ static const struct edid_quirk {
 	/* LGD panel of HP zBook 17 G2, eDP 10 bpc, but reports unknown bpc */
 	{ "LGD", 764, EDID_QUIRK_FORCE_10BPC },
 
+	/* LGD panel of Lenovo L540 reports 8 bpc, but is a 6 bpc panel */
+	{ "LGD", 0x038e, EDID_QUIRK_FORCE_6BPC },
+
 	/* LG Philips LCD LP154W01-A5 */
 	{ "LPL", 0, EDID_QUIRK_DETAILED_USE_MAXIMUM_SIZE },
 	{ "LPL", 0x2a00, EDID_QUIRK_DETAILED_USE_MAXIMUM_SIZE },
-- 
2.30.2


-- 
Francesco P. Lovergine
