[PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[John Foushee]

Commit 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight possible
check condition") restricted the VESA backlight path to fully AUX-based
panels (enable and adjustment both via AUX), on the grounds that the
hybrid configurations are not currently supported.

The hybrid pin-enable + AUX-adjustment configuration is however already
handled: intel_dp_aux_vesa_enable_backlight() falls back to the PWM
funcs for enable when info.aux_enable is unset, and
drm_edp_backlight_init() supports aux_set without aux_enable.

At least one panel requires this configuration to work at all: the
Tianma Y156ZAN02.0 in the Google Pixel Slate (nocturne) advertises
DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP but not
DP_EDP_BACKLIGHT_AUX_ENABLE_CAP (DP_EDP_GENERAL_CAP_1 = 0xfb,
DP_EDP_BACKLIGHT_ADJUSTMENT_CAP = 0xff). The panel ignores the PWM pin
for brightness adjustment, and resets its AUX brightness register
(DP_EDP_BACKLIGHT_BRIGHTNESS_MSB/LSB) to 0 whenever panel power is
cycled. With the PWM backlight funcs selected, the panel comes back
black after every suspend/resume or DPMS off/on cycle while all
driver-visible state (link training, PPS, PWM duty) looks healthy.
Firmware rewrites the register at boot, which masks the problem until
the first runtime panel power cycle.

Allow the hybrid configuration by requiring only AUX brightness
adjustment capability; backlight enable keeps using the pin/PWM path
via the existing fallback.

Tested on the Google Pixel Slate (KBL-Y) on 7.1.4: i915 now selects the
VESA AUX backlight interface, the panel's AUX brightness register is
restored across suspend/resume, and brightness control works over the
full range where it previously had no effect.

Fixes: 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight possible check condition")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679
Cc: stable@vger.kernel.org
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: John Foushee <johnfoushee@gmail.com>
---
 .../gpu/drm/i915/display/intel_dp_aux_backlight.c    | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

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 7a6c07f..a5c03c3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -616,11 +616,15 @@ check_if_vesa_backlight_possible(struct intel_dp *intel_dp)
 	u8 bit_min, bit_max;
 
 	/*
-	 * Since we only support Fully AUX Based VESA Backlight interface make sure
-	 * backlight enable is possible via AUX along with backlight adjustment
+	 * Brightness adjustment must be possible via AUX. Backlight *enable*
+	 * may come either via AUX (DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) or via the
+	 * BL_ENABLE pin, which the VESA backlight code already supports by
+	 * falling back to the PWM funcs for enable when aux_enable is not set.
+	 * Some panels (e.g. Tianma Y156ZAN02.0 in the Google Pixel Slate)
+	 * support only that hybrid configuration and ignore the PWM pin for
+	 * brightness adjustment.
 	 */
-	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP &&
-	      intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
+	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
 		return false;
 
 	ret = drm_dp_dpcd_read_byte(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
-- 
2.47.3

RE: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[Kandpal, Suraj]

> Subject: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness
> panels
> 
> Commit 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight possible check
> condition") restricted the VESA backlight path to fully AUX-based panels
> (enable and adjustment both via AUX), on the grounds that the hybrid
> configurations are not currently supported.
> 
> The hybrid pin-enable + AUX-adjustment configuration is however already
> handled: intel_dp_aux_vesa_enable_backlight() falls back to the PWM funcs
> for enable when info.aux_enable is unset, and
> drm_edp_backlight_init() supports aux_set without aux_enable.
> 
> At least one panel requires this configuration to work at all: the Tianma
> Y156ZAN02.0 in the Google Pixel Slate (nocturne) advertises
> DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP but not
> DP_EDP_BACKLIGHT_AUX_ENABLE_CAP (DP_EDP_GENERAL_CAP_1 = 0xfb,
> DP_EDP_BACKLIGHT_ADJUSTMENT_CAP = 0xff). The panel ignores the PWM
> pin for brightness adjustment, and resets its AUX brightness register
> (DP_EDP_BACKLIGHT_BRIGHTNESS_MSB/LSB) to 0 whenever panel power is
> cycled. With the PWM backlight funcs selected, the panel comes back black
> after every suspend/resume or DPMS off/on cycle while all driver-visible state
> (link training, PPS, PWM duty) looks healthy.
> Firmware rewrites the register at boot, which masks the problem until the first
> runtime panel power cycle.
> 
> Allow the hybrid configuration by requiring only AUX brightness adjustment
> capability; backlight enable keeps using the pin/PWM path via the existing
> fallback.
> 
> Tested on the Google Pixel Slate (KBL-Y) on 7.1.4: i915 now selects the VESA
> AUX backlight interface, the panel's AUX brightness register is restored across
> suspend/resume, and brightness control works over the full range where it
> previously had no effect.
> 
> Fixes: 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight possible check
> condition")
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679
> Cc: stable@vger.kernel.org
> Cc: Suraj Kandpal <suraj.kandpal@intel.com>
> Signed-off-by: John Foushee <johnfoushee@gmail.com>

Hi John this fix has been already floated, reviewed and merged some days ago to drm-intel-next.

https://patchwork.freedesktop.org/series/170522/

Regards,
Suraj Kandpal

> ---
>  .../gpu/drm/i915/display/intel_dp_aux_backlight.c    | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> 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 7a6c07f..a5c03c3 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -616,11 +616,15 @@ check_if_vesa_backlight_possible(struct intel_dp
> *intel_dp)
>  	u8 bit_min, bit_max;
> 
>  	/*
> -	 * Since we only support Fully AUX Based VESA Backlight interface make
> sure
> -	 * backlight enable is possible via AUX along with backlight adjustment
> +	 * Brightness adjustment must be possible via AUX. Backlight *enable*
> +	 * may come either via AUX (DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> or via the
> +	 * BL_ENABLE pin, which the VESA backlight code already supports by
> +	 * falling back to the PWM funcs for enable when aux_enable is not set.
> +	 * Some panels (e.g. Tianma Y156ZAN02.0 in the Google Pixel Slate)
> +	 * support only that hybrid configuration and ignore the PWM pin for
> +	 * brightness adjustment.
>  	 */
> -	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
> &&
> -	      intel_dp->edp_dpcd[2] &
> DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> +	if (!(intel_dp->edp_dpcd[2] &
> +DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
>  		return false;
> 
>  	ret = drm_dp_dpcd_read_byte(&intel_dp->aux,
> DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
> --
> 2.47.3

Re: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[John Foushee]

> Hi John this fix has been already floated, reviewed and merged some days
> ago to drm-intel-next.
>
> https://patchwork.freedesktop.org/series/170522/

Thanks, glad it's fixed, and happy to see the same conclusion; please
disregard my patch.

For the record: independently root-caused and tested the same change on a
Google Pixel Slate (nocturne, Tianma Y156ZAN02.0: advertises
BRIGHTNESS_AUX_SET_CAP without AUX_ENABLE_CAP, ignores PWM for brightness,
and resets the AUX brightness register on every panel power cycle, so it
resumes from suspend to a permanently black screen without this fix). With
the equivalent change on 7.1.4 the panel's AUX brightness register is
restored across suspend/resume and full-range brightness control works,
so feel free to count that as a

Tested-by: John Foushee <johnfoushee@gmail.com>

for commit 7d594b24 on real affected hardware.

One question: the regression (ed8be780bdbc upstream / 102d44b3a8fa in
mainline) is present in the shipping 7.1.x stable series, but 7d594b24
doesn't carry Cc: stable. Will the Fixes: tag be enough for it to be picked
up for 7.1.x/7.2.x, or should it be nominated to stable explicitly?
Affected devices are unusable after any suspend without it, so a backport
would matter to users on current stable kernels.

Diagnosis details, DPCD dumps and EDID, if useful:
https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679

Thanks,
John


On Wed, Jul 22, 2026 at 9:22 AM Kandpal, Suraj <suraj.kandpal@intel.com> wrote:
>
>
> > Subject: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness
> > panels
> >
> > Commit 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight possible check
> > condition") restricted the VESA backlight path to fully AUX-based panels
> > (enable and adjustment both via AUX), on the grounds that the hybrid
> > configurations are not currently supported.
> >
> > The hybrid pin-enable + AUX-adjustment configuration is however already
> > handled: intel_dp_aux_vesa_enable_backlight() falls back to the PWM funcs
> > for enable when info.aux_enable is unset, and
> > drm_edp_backlight_init() supports aux_set without aux_enable.
> >
> > At least one panel requires this configuration to work at all: the Tianma
> > Y156ZAN02.0 in the Google Pixel Slate (nocturne) advertises
> > DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP but not
> > DP_EDP_BACKLIGHT_AUX_ENABLE_CAP (DP_EDP_GENERAL_CAP_1 = 0xfb,
> > DP_EDP_BACKLIGHT_ADJUSTMENT_CAP = 0xff). The panel ignores the PWM
> > pin for brightness adjustment, and resets its AUX brightness register
> > (DP_EDP_BACKLIGHT_BRIGHTNESS_MSB/LSB) to 0 whenever panel power is
> > cycled. With the PWM backlight funcs selected, the panel comes back black
> > after every suspend/resume or DPMS off/on cycle while all driver-visible state
> > (link training, PPS, PWM duty) looks healthy.
> > Firmware rewrites the register at boot, which masks the problem until the first
> > runtime panel power cycle.
> >
> > Allow the hybrid configuration by requiring only AUX brightness adjustment
> > capability; backlight enable keeps using the pin/PWM path via the existing
> > fallback.
> >
> > Tested on the Google Pixel Slate (KBL-Y) on 7.1.4: i915 now selects the VESA
> > AUX backlight interface, the panel's AUX brightness register is restored across
> > suspend/resume, and brightness control works over the full range where it
> > previously had no effect.
> >
> > Fixes: 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight possible check
> > condition")
> > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679
> > Cc: stable@vger.kernel.org
> > Cc: Suraj Kandpal <suraj.kandpal@intel.com>
> > Signed-off-by: John Foushee <johnfoushee@gmail.com>
>
> Hi John this fix has been already floated, reviewed and merged some days ago to drm-intel-next.
>
> https://patchwork.freedesktop.org/series/170522/
>
> Regards,
> Suraj Kandpal
>
> > ---
> >  .../gpu/drm/i915/display/intel_dp_aux_backlight.c    | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > 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 7a6c07f..a5c03c3 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -616,11 +616,15 @@ check_if_vesa_backlight_possible(struct intel_dp
> > *intel_dp)
> >       u8 bit_min, bit_max;
> >
> >       /*
> > -      * Since we only support Fully AUX Based VESA Backlight interface make
> > sure
> > -      * backlight enable is possible via AUX along with backlight adjustment
> > +      * Brightness adjustment must be possible via AUX. Backlight *enable*
> > +      * may come either via AUX (DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> > or via the
> > +      * BL_ENABLE pin, which the VESA backlight code already supports by
> > +      * falling back to the PWM funcs for enable when aux_enable is not set.
> > +      * Some panels (e.g. Tianma Y156ZAN02.0 in the Google Pixel Slate)
> > +      * support only that hybrid configuration and ignore the PWM pin for
> > +      * brightness adjustment.
> >        */
> > -     if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
> > &&
> > -           intel_dp->edp_dpcd[2] &
> > DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> > +     if (!(intel_dp->edp_dpcd[2] &
> > +DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> >               return false;
> >
> >       ret = drm_dp_dpcd_read_byte(&intel_dp->aux,
> > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
> > --
> > 2.47.3
>


-- 

@foush

RE: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[Kandpal, Suraj]

> Subject: Re: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX
> brightness panels
> 
> > Hi John this fix has been already floated, reviewed and merged some
> > days ago to drm-intel-next.
> >
> > https://patchwork.freedesktop.org/series/170522/
> 
> Thanks, glad it's fixed, and happy to see the same conclusion; please disregard
> my patch.
> 
> For the record: independently root-caused and tested the same change on a
> Google Pixel Slate (nocturne, Tianma Y156ZAN02.0: advertises
> BRIGHTNESS_AUX_SET_CAP without AUX_ENABLE_CAP, ignores PWM for
> brightness, and resets the AUX brightness register on every panel power cycle,
> so it resumes from suspend to a permanently black screen without this fix).
> With the equivalent change on 7.1.4 the panel's AUX brightness register is
> restored across suspend/resume and full-range brightness control works, so
> feel free to count that as a
> 

Hi Thanks for the patch, yes I had a lot of gitlab from panels that don’t have a PWM fallback which led to this same fix.

> Tested-by: John Foushee <johnfoushee@gmail.com>
> 
> for commit 7d594b24 on real affected hardware.
> 
> One question: the regression (ed8be780bdbc upstream / 102d44b3a8fa in
> mainline) is present in the shipping 7.1.x stable series, but 7d594b24 doesn't
> carry Cc: stable. Will the Fixes: tag be enough for it to be picked up for
> 7.1.x/7.2.x, or should it be nominated to stable explicitly?
> Affected devices are unusable after any suspend without it, so a backport
> would matter to users on current stable kernels.

Yes I just Cc'ed them so that it gets picked up. Added you in it too.

Regards,
Suraj Kandpal

> 
> Diagnosis details, DPCD dumps and EDID, if useful:
> https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679
> 
> Thanks,
> John
> 
> 
> On Wed, Jul 22, 2026 at 9:22 AM Kandpal, Suraj <suraj.kandpal@intel.com>
> wrote:
> >
> >
> > > Subject: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX
> > > brightness panels
> > >
> > > Commit 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight
> > > possible check
> > > condition") restricted the VESA backlight path to fully AUX-based
> > > panels (enable and adjustment both via AUX), on the grounds that the
> > > hybrid configurations are not currently supported.
> > >
> > > The hybrid pin-enable + AUX-adjustment configuration is however
> > > already
> > > handled: intel_dp_aux_vesa_enable_backlight() falls back to the PWM
> > > funcs for enable when info.aux_enable is unset, and
> > > drm_edp_backlight_init() supports aux_set without aux_enable.
> > >
> > > At least one panel requires this configuration to work at all: the
> > > Tianma
> > > Y156ZAN02.0 in the Google Pixel Slate (nocturne) advertises
> > > DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP but not
> > > DP_EDP_BACKLIGHT_AUX_ENABLE_CAP (DP_EDP_GENERAL_CAP_1 = 0xfb,
> > > DP_EDP_BACKLIGHT_ADJUSTMENT_CAP = 0xff). The panel ignores the
> PWM
> > > pin for brightness adjustment, and resets its AUX brightness
> > > register
> > > (DP_EDP_BACKLIGHT_BRIGHTNESS_MSB/LSB) to 0 whenever panel power
> is
> > > cycled. With the PWM backlight funcs selected, the panel comes back
> > > black after every suspend/resume or DPMS off/on cycle while all
> > > driver-visible state (link training, PPS, PWM duty) looks healthy.
> > > Firmware rewrites the register at boot, which masks the problem
> > > until the first runtime panel power cycle.
> > >
> > > Allow the hybrid configuration by requiring only AUX brightness
> > > adjustment capability; backlight enable keeps using the pin/PWM path
> > > via the existing fallback.
> > >
> > > Tested on the Google Pixel Slate (KBL-Y) on 7.1.4: i915 now selects
> > > the VESA AUX backlight interface, the panel's AUX brightness
> > > register is restored across suspend/resume, and brightness control
> > > works over the full range where it previously had no effect.
> > >
> > > Fixes: 102d44b3a8fa ("drm/i915/backlight: Fix VESA backlight
> > > possible check
> > > condition")
> > > Closes:
> > > https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679
> > > Cc: stable@vger.kernel.org
> > > Cc: Suraj Kandpal <suraj.kandpal@intel.com>
> > > Signed-off-by: John Foushee <johnfoushee@gmail.com>
> >
> > Hi John this fix has been already floated, reviewed and merged some days
> ago to drm-intel-next.
> >
> > https://patchwork.freedesktop.org/series/170522/
> >
> > Regards,
> > Suraj Kandpal
> >
> > > ---
> > >  .../gpu/drm/i915/display/intel_dp_aux_backlight.c    | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > >
> > > 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 7a6c07f..a5c03c3 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > @@ -616,11 +616,15 @@ check_if_vesa_backlight_possible(struct
> > > intel_dp
> > > *intel_dp)
> > >       u8 bit_min, bit_max;
> > >
> > >       /*
> > > -      * Since we only support Fully AUX Based VESA Backlight interface make
> > > sure
> > > -      * backlight enable is possible via AUX along with backlight adjustment
> > > +      * Brightness adjustment must be possible via AUX. Backlight *enable*
> > > +      * may come either via AUX (DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> > > or via the
> > > +      * BL_ENABLE pin, which the VESA backlight code already supports by
> > > +      * falling back to the PWM funcs for enable when aux_enable is not set.
> > > +      * Some panels (e.g. Tianma Y156ZAN02.0 in the Google Pixel Slate)
> > > +      * support only that hybrid configuration and ignore the PWM pin for
> > > +      * brightness adjustment.
> > >        */
> > > -     if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP
> > > &&
> > > -           intel_dp->edp_dpcd[2] &
> > > DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> > > +     if (!(intel_dp->edp_dpcd[2] &
> > > +DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> > >               return false;
> > >
> > >       ret = drm_dp_dpcd_read_byte(&intel_dp->aux,
> > > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &bit_min);
> > > --
> > > 2.47.3
> >
> 
> 
> --
> 
> @foush

Re: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Hybrid eDP panels supporting luminance control (luminance_set == true) but lacking AUX enable capability (aux_enable == false) will fail to turn on the backlight.
--

--- Patch [1]: [PATCH] drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels ---
commit 5c1988c15272e150c5abfa3acb528c1a51340cb5
Author: John Foushee <johnfoushee@gmail.com>

    drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

This commit allows the use of hybrid eDP backlight configurations (where
brightness is adjusted via AUX but enablement happens via the BL_ENABLE PWM
pin) by dropping the DP_EDP_BACKLIGHT_AUX_ENABLE_CAP requirement in the VESA
backlight check.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/16679

> 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 7a6c07f6aaeb4..a5c03c32a7d43 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -616,11 +616,15 @@ check_if_vesa_backlight_possible(struct intel_dp *intel_dp)
>  	u8 bit_min, bit_max;
>  
>  	/*
> -	 * Since we only support Fully AUX Based VESA Backlight interface make sure
> -	 * backlight enable is possible via AUX along with backlight adjustment
> +	 * Brightness adjustment must be possible via AUX. Backlight *enable*
> +	 * may come either via AUX (DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) or via the
> +	 * BL_ENABLE pin, which the VESA backlight code already supports by
> +	 * falling back to the PWM funcs for enable when aux_enable is not set.

[Severity: High]
This is a pre-existing issue, but does the PWM fallback actually execute for
panels with luminance control?

Looking at the existing logic in intel_dp_aux_vesa_enable_backlight():

	if (!(panel->backlight.edp.vesa.info.aux_enable ||
	      panel->backlight.edp.vesa.info.luminance_set)) {
		u32 pwm_level;
		// ... (PWM fallback enable code)

If an eDP panel supports luminance control (luminance_set == true) but lacks
AUX enable capability (aux_enable == false), wouldn't this condition evaluate
to false, skipping the PWM fallback entirely?

If the fallback is skipped, the backlight enable pin won't be asserted via
PWM, and the AUX enablement won't happen since aux_enable is false. Could
this cause such panels to remain permanently black and unusable?

> +	 * Some panels (e.g. Tianma Y156ZAN02.0 in the Google Pixel Slate)
> +	 * support only that hybrid configuration and ignore the PWM pin for
> +	 * brightness adjustment.
>  	 */
> -	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP &&
> -	      intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
> +	if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP))
>  		return false;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260722154802.3760046-1-johnfoushee@gmail.com?part=1

✗ LGCI.VerificationFailed: failure for drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[Patchwork]

== Series Details ==

Series: drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels
URL   : https://patchwork.freedesktop.org/series/170998/
State : failure

== Summary ==

Series author address 'johnfoushee@gmail.com' is not on the allowlist, which prevents CI from being automatically triggered.
If you want CI to run for this series, ask Patchwork project owners to click 'retest' on the series in Patchwork.
Exception occurred during validation, bailing out!
Build URL: http://intel-gfx-ci-public.igk.intel.com:8080/job/xe_pw_trigger/1223750/ (on master)

✗ LGCI.VerificationFailed: failure for drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels

[Patchwork]

== Series Details ==

Series: drm/i915/backlight: allow hybrid pin-enable + AUX brightness panels
URL   : https://patchwork.freedesktop.org/series/171000/
State : failure

== Summary ==

Series author address 'johnfoushee@gmail.com' is not on the allowlist, which prevents CI from being automatically triggered.
If you want CI to run for this series, ask Patchwork project owners to click 'retest' on the series in Patchwork.
Exception occurred during validation, bailing out!
Build URL: http://gfx-ci.igk.intel.com:8080/job/CI_PW_kernel/181971/ (on built-in)