On Fri, 17 Jan 2020, Jani Nikula <jani.nikula@xxxxxxxxx> wrote: > 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. So I've gone ahead and pushed patches 1-3 and 5 in this series, as they were tested as part of the series I posted. BR, Jani. > > 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 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
