linux-kernel - [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46

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Message-Id: <20220721152314.RFC.1.Ie333b3e4aff6e4a5b58c4aa805e030e561be8773@changeid>
Date:   Thu, 21 Jul 2022 15:23:40 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     dri-devel@...ts.freedesktop.org
Cc:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        freedreno@...ts.freedesktop.org,
        Douglas Anderson <dianders@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46

The Sharp LQ140M1JW46 panel is on the Qualcomm sc7280 CRD reference
board. This panel supports 144 Hz and 60 Hz. In the EDID, the 144 Hz
mode is listed first and thus is marked preferred. The EDID decode I
ran says:

  First detailed timing includes the native pixel format and preferred
  refresh rate.

  ...

  Detailed Timing Descriptors:
    DTD 1:  1920x1080  143.981 Hz  16:9   166.587 kHz  346.500 MHz
                 Hfront   48 Hsync  32 Hback  80 Hpol N
                 Vfront    3 Vsync   5 Vback  69 Vpol N
    DTD 2:  1920x1080   59.990 Hz  16:9    69.409 kHz  144.370 MHz
                 Hfront   48 Hsync  32 Hback  80 Hpol N
                 Vfront    3 Vsync   5 Vback  69 Vpol N

I'm proposing here that the above is actually a bug and that the 60 Hz
mode really should be considered preferred by Linux.

The argument here is that this is a laptop panel and on a laptop we
know power will always be a concern. Presumably even if someone using
this panel wanted to use 144 Hz for some use cases they would only do
so dynamically and would still want the default to be 60 Hz.

Let's change the default to 60 Hz using a standard quirk.

Signed-off-by: Douglas Anderson <dianders@...omium.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 bbc25e3b7220..06ff8ba216af 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -160,6 +160,9 @@ static const struct edid_quirk {
 	EDID_QUIRK('S', 'A', 'M', 596, EDID_QUIRK_PREFER_LARGE_60),
 	EDID_QUIRK('S', 'A', 'M', 638, EDID_QUIRK_PREFER_LARGE_60),
 
+	/* 144 Hz should only be used when needed; it wastes power */
+	EDID_QUIRK('S', 'H', 'P', 0x1523, EDID_QUIRK_PREFER_LARGE_60),
+
 	/* Sony PVM-2541A does up to 12 bpc, but only reports max 8 bpc */
 	EDID_QUIRK('S', 'N', 'Y', 0x2541, EDID_QUIRK_FORCE_12BPC),
 
-- 
2.37.1.359.gd136c6c3e2-goog