Re: [PATCH v3 1/1] drm/i915/display: Add quirk to force backlight type on some TUXEDO devices

From: Werner Sembach

Date: Fri Aug 07 2026 - 14:10:07 EST

Hi,

Am 07.08.26 um 04:37 schrieb Kandpal, Suraj:
Subject: Re: [PATCH v3 1/1] drm/i915/display: Add quirk to force backlight type
on some TUXEDO devices

Am 04.08.26 um 21:52 schrieb Werner Sembach:

The display backlight on TUXEDO DX1708 and InsanityBook 15 v1 with
panels AUO 12701 and AUO 12701 must be forced to
INTEL_DP_AUX_BACKLIGHT_ON to be able to control the brightness.
You need to mention why that is
"Because the broken VBT in these panels report INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE
even though the only way to control them is via Intel's backlight interface. Which means'
the VBT should ideally report INTEL_BACKLIGHT_DISPLAY_DDI in its params"
ok will add

This could already be archived via a module parameter, but this patch
* can already
* achieved
thanks for spotting

adds a quirk to apply this by default on the mentioned devices.

This patch does not actually test for the exact panels as the id that
is used in the intel_dpcd_quirks list is sadly zeroed on the devices,
but afaik all these devices use try_intel_interface first anyway so
all the quirk does is to add the fallback to try_vesa_interface, so
the behaviour on the devices not needing the quirk and fallback should
functionally stay the same.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Werner Sembach <wse@xxxxxxxxxxxxxxxxxxx>
Fixes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/15679

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/15679

---
.../drm/i915/display/intel_dp_aux_backlight.c | 9 ++++++-
drivers/gpu/drm/i915/display/intel_quirks.c | 24 +++++++++++++++++++
drivers/gpu/drm/i915/display/intel_quirks.h | 1 +
3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index 266e042e00237..594c59f2d8309 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -41,6 +41,7 @@
#include "intel_display_types.h"
#include "intel_dp.h"
#include "intel_dp_aux_backlight.h"
+#include "intel_quirks.h"

/*
* DP AUX registers for Intel's proprietary HDR backlight interface.
We define @@ -687,11 +688,17 @@ int
intel_dp_aux_init_backlight_funcs(struct intel_connector *connector)
struct drm_device *dev = connector->base.dev;
struct intel_panel *panel = &connector->panel;
bool try_intel_interface = false, try_vesa_interface = false;
+ int enable_dpcd_backlight;

/* Check the VBT and user's module parameters to figure out which
* interfaces to probe
*/
This comment need to be moved just above the switch()
ok

- switch (display->params.enable_dpcd_backlight) {
+ enable_dpcd_backlight = display->params.enable_dpcd_backlight;
+ if (enable_dpcd_backlight == INTEL_DP_AUX_BACKLIGHT_AUTO &&
+ intel_has_dpcd_quirk(intel_dp, QUIRK_ENABLE_DPCD_BACKLIGHT))
+ enable_dpcd_backlight = INTEL_DP_AUX_BACKLIGHT_ON;
Let's also have a comment here as to why a quirk was used instead of just making VESA the default interface.
This will help developers avoid going through a series of regressions, fixes and inevitable reverts.

ok i try my best to formulate something

v4 incoming, thanks for the review

Werner Sembach


Regards,
Suraj Kandpal
+
+ switch (enable_dpcd_backlight) {
case INTEL_DP_AUX_BACKLIGHT_OFF:
return -ENODEV;
case INTEL_DP_AUX_BACKLIGHT_AUTO:
diff --git a/drivers/gpu/drm/i915/display/intel_quirks.c
b/drivers/gpu/drm/i915/display/intel_quirks.c
index 33245f44c0d50..89d82364ae45d 100644
--- a/drivers/gpu/drm/i915/display/intel_quirks.c
+++ b/drivers/gpu/drm/i915/display/intel_quirks.c
@@ -100,6 +100,14 @@ static void quirk_disable_psr2(struct intel_display
*display)
drm_info(display->drm, "PSR2 support not currently available for this
setup, applying disable PSR2 quirk\n");
}

+static void quirk_enable_dpcd_backlight(struct intel_dp *intel_dp) {
+ struct intel_display *display = to_intel_display(intel_dp);
+
+ intel_set_dpcd_quirk(intel_dp, QUIRK_ENABLE_DPCD_BACKLIGHT);
+ drm_info(display->drm, "Applying Enable DPCD Backlight quirk\n"); }
+
struct intel_quirk {
int device;
int subsystem_vendor;
@@ -286,6 +294,22 @@ static const struct intel_dpcd_quirk
intel_dpcd_quirks[] = {
.sink_oui = SINK_OUI(0x00, 0x22, 0xb9),
.hook = quirk_disable_edp_panel_replay,
},
+ /* TUXEDO InsanityBook 15 v1 */
+ {
+ .device = 0x591b,
+ .subsystem_vendor = 0x1558,
+ .subsystem_device = 0x9501,
+ .sink_oui = SINK_OUI(0x38, 0xec, 0x11),
+ .hook = quirk_enable_dpcd_backlight,
+ },
+ /* TUXEDO DX1708 */
+ {
+ .device = 0x3e9b,
+ .subsystem_vendor = 0x1558,
+ .subsystem_device = 0x8500,
+ .sink_oui = SINK_OUI(0x38, 0xec, 0x11),
+ .hook = quirk_enable_dpcd_backlight,
+ },
};

void intel_init_quirks(struct intel_display *display) diff --git
a/drivers/gpu/drm/i915/display/intel_quirks.h
b/drivers/gpu/drm/i915/display/intel_quirks.h
index 970a4fe52fafc..4996419ae76bd 100644
--- a/drivers/gpu/drm/i915/display/intel_quirks.h
+++ b/drivers/gpu/drm/i915/display/intel_quirks.h
@@ -23,6 +23,7 @@ enum intel_quirk_id {
QUIRK_EDP_LIMIT_RATE_HBR2,
QUIRK_DISABLE_EDP_PANEL_REPLAY,
QUIRK_DISABLE_PSR2,
+ QUIRK_ENABLE_DPCD_BACKLIGHT,
};

void intel_init_quirks(struct intel_display *display);