On 5/17/26 04:47, Suraj Kandpal wrote:
> This reverts commit 40d2f5820951dee818d05c14677277048bd85f9f.
>
> Removing the try_vesa_interface gate caused a backlight regression on
> panels whose VBT correctly reports INTEL_BACKLIGHT_DISPLAY_DDI and whose
> PWM path is the actual backlight control, but whose DPCD optimistically
> advertises DP_EDP_BACKLIGHT_AUX_ENABLE_CAP / _BRIGHTNESS_AUX_SET_CAP.
> After the commit such panels silently bind to the VESA AUX backlight
> funcs; AUX writes complete but the panel ignores them, leaving
> brightness stuck (no-op backlight). Observed on at least KBL and TGL
> eDP setups.
Lo! What's the status of this regression fix? It's a -next for two weeks
now as f30fddb4402313 ("Revert "drm/i915/backlight: Remove
try_vesa_interface""), but from the outside and checking
https://gitlab.freedesktop.org/drm/i915/kernel/-/commits/drm-intel-fixes
it looks like it's scheduled for merging in the next cycle.
But I think it should be merged this cycle (ideally before -rc7, as
Linus wants all known regression fixed by -rc6), as it fixes a
regression that is known since the -rc1 days. I already asked for the
mainlining plans in gitlab tickets about a week ago (and since then
affected users spoke up, too), but there was no conclusive answer for
the plans, which is why I'm trying this way now.
Ciao, Thorsten
> Signed-off-by: Suraj Kandpal <[email protected]>
> ---
> .../drm/i915/display/intel_dp_aux_backlight.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 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 a8d56ebf06a2..7a6c07f6aaeb 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -691,10 +691,9 @@ int intel_dp_aux_init_backlight_funcs(struct
> intel_connector *connector)
> struct intel_dp *intel_dp = intel_attached_dp(connector);
> struct drm_device *dev = connector->base.dev;
> struct intel_panel *panel = &connector->panel;
> - bool try_intel_interface = false;
> + bool try_intel_interface = false, try_vesa_interface = false;
>
> - /*
> - * Check the VBT and user's module parameters to figure out which
> + /* Check the VBT and user's module parameters to figure out which
> * interfaces to probe
> */
> switch (display->params.enable_dpcd_backlight) {
> @@ -703,6 +702,7 @@ int intel_dp_aux_init_backlight_funcs(struct
> intel_connector *connector)
> case INTEL_DP_AUX_BACKLIGHT_AUTO:
> switch (panel->vbt.backlight.type) {
> case INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE:
> + try_vesa_interface = true;
> break;
> case INTEL_BACKLIGHT_DISPLAY_DDI:
> try_intel_interface = true;
> @@ -715,12 +715,20 @@ int intel_dp_aux_init_backlight_funcs(struct
> intel_connector *connector)
> if (panel->vbt.backlight.type !=
> INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)
> try_intel_interface = true;
>
> + try_vesa_interface = true;
> + break;
> + case INTEL_DP_AUX_BACKLIGHT_FORCE_VESA:
> + try_vesa_interface = true;
> break;
> case INTEL_DP_AUX_BACKLIGHT_FORCE_INTEL:
> try_intel_interface = true;
> break;
> }
>
> + /* For eDP 1.5 and above we are supposed to use VESA interface for
> brightness control */
> + if (intel_dp->edp_dpcd[0] >= DP_EDP_15)
> + try_vesa_interface = true;
> +
> /*
> * Since Intel has their own backlight control interface, the majority
> of machines out there
> * using DPCD backlight controls with Intel GPUs will be using this
> interface as opposed to
> @@ -733,9 +741,6 @@ int intel_dp_aux_init_backlight_funcs(struct
> intel_connector *connector)
> * panel with Intel's OUI - which is also required for us to be able to
> detect Intel's
> * backlight interface at all. This means that the only sensible way
> for us to detect both
> * interfaces is to probe for Intel's first, and VESA's second.
> - *
> - * Also there is a chance some VBTs may advertise false Intel backlight
> support even if the
> - * TCON DPCD says otherwise. This means we keep VESA interface as
> fallback in that case.
> */
> if (try_intel_interface && intel_dp->edp_dpcd[0] <= DP_EDP_14b &&
> intel_dp_aux_supports_hdr_backlight(connector)) {
> @@ -745,7 +750,7 @@ int intel_dp_aux_init_backlight_funcs(struct
> intel_connector *connector)
> return 0;
> }
>
> - if (intel_dp_aux_supports_vesa_backlight(connector)) {
> + if (try_vesa_interface &&
> intel_dp_aux_supports_vesa_backlight(connector)) {
> drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using VESA eDP backlight
> controls\n",
> connector->base.base.id, connector->base.name);
> panel->backlight.funcs = &intel_dp_vesa_bl_funcs;
