On Thu, 16 Jan 2020, Lyude Paul <lyude@xxxxxxxxxx> wrote: > Despite the fact that the VBT appears to have a field for specifying > that a system is equipped with a panel that supports standard VESA > backlight controls over the DP AUX channel, so far every system we've > spotted DPCD backlight control support on doesn't actually set this > field correctly and all have it set to INTEL_BACKLIGHT_DISPLAY_DDI. > > While we don't know the exact reason for this VBT misuse, talking with > some vendors indicated that there's a good number of laptop panels out > there that supposedly support both PWM backlight controls and DPCD > backlight controls as a workaround until Intel supports DPCD backlight > controls across platforms universally. This being said, the X1 Extreme > 2nd Gen that I have here (note that Lenovo is not the hardware vendor > that informed us of this) PWM backlight controls are advertised, but > only DPCD controls actually function. I'm going to make an educated > guess here and say that on systems like this one, it's likely that PWM > backlight controls might have been intended to work but were never > really tested by QA. > > Since we really need backlights to work without any extra module > parameters, let's take the risk here and rely on the standard DPCD caps > to tell us whether AUX backlight controls are supported or not. We still > check the VBT, but only to make sure that we don't enable DPCD backlight > controls on a panel that uses something other then the standard VESA > interfaces over AUX. Since panels using such non-standard interfaces > should probably have support added to i915, we'll print a warning when > seeing this in the VBT. We can remove this warning later if we end up > adding support for any custom backlight interfaces. > > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112376 > Cc: Jani Nikula <jani.nikula@xxxxxxxxx> > Cc: Perry Yuan <pyuan@xxxxxxxxxx> > Cc: AceLan Kao <acelan.kao@xxxxxxxxxxxxx> > --- > .../drm/i915/display/intel_dp_aux_backlight.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 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 77a759361c5c..3002b600635f 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > @@ -330,13 +330,17 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector) > struct intel_panel *panel = &intel_connector->panel; > struct drm_i915_private *dev_priv = to_i915(intel_connector->base.dev); > > - if (i915_modparams.enable_dpcd_backlight == 0 || > - (i915_modparams.enable_dpcd_backlight == -1 && > - dev_priv->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)) > - return -ENODEV; > - > - if (!intel_dp_aux_display_control_capable(intel_connector)) > + if (i915_modparams.enable_dpcd_backlight == 0) > return -ENODEV; > + if (i915_modparams.enable_dpcd_backlight == -1) { > + if (dev_priv->vbt.backlight.type > + == INTEL_BACKLIGHT_PANEL_DRIVER_INTERFACE) { > + DRM_WARN("VBT says panel uses custom panel driver interface, not using DPCD backlight controls\n"); > + return -ENODEV; > + } > + if (!intel_dp_aux_display_control_capable(intel_connector)) > + return -ENODEV; Functionally, I'm fine with trying this. But perhaps we should check aux and early return first, and then check what vbt says, to reduce the dmesg noise. I'll probably want to see a debug message if we're enabling aux backlight even if dev_priv->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE. It's the kind of debug trace you'll really want to get first. BR, Jani. > + } > > panel->backlight.setup = intel_dp_aux_setup_backlight; > panel->backlight.enable = intel_dp_aux_enable_backlight; -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
