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, just so we can print a debugging message on systems that advertise DPCD backlight support on the panel but not in the VBT.
Changes since v3: * Print a debugging message if we enable DPCD backlight control on a device which doesn't report DPCD backlight controls in it's VBT, instead of warning on custom panel backlight interfaces.
Signed-off-by: Lyude Paul lyude@redhat.com Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112376 Cc: Jani Nikula jani.nikula@intel.com Cc: Perry Yuan pyuan@redhat.com Cc: AceLan Kao acelan.kao@canonical.com --- drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 9 +++++---- 1 file changed, 5 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 77a759361c5c..0f8edc775375 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c @@ -328,15 +328,16 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector) 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); + enum intel_backlight_type type = + to_i915(intel_connector->base.dev)->vbt.backlight.type;
if (i915_modparams.enable_dpcd_backlight == 0 || (i915_modparams.enable_dpcd_backlight == -1 && - dev_priv->vbt.backlight.type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE)) + !intel_dp_aux_display_control_capable(intel_connector))) return -ENODEV;
- if (!intel_dp_aux_display_control_capable(intel_connector)) - return -ENODEV; + if (type != INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE) + DRM_DEBUG_DRIVER("Ignoring VBT backlight type\n");
panel->backlight.setup = intel_dp_aux_setup_backlight; panel->backlight.enable = intel_dp_aux_enable_backlight;