On Fri, 22 Nov 2019, Lyude Paul <ly...@redhat.com> wrote:
> Annoyingly, the VBT on the ThinkPad X1 Extreme 2nd Gen indicates that
> the system uses plain PWM based backlight controls, when in reality the
> only backlight controls that work are the standard VESA eDP DPCD
> backlight controls.
>
> Honestly, this makes me wonder how many other systems have these issues
> or lie about this in their VBT. Not sure we have any good way of finding
> out until panels like this become more common place in the laptop
> market. For now, just add a DRM DP quirk to indicate that this panel is
> telling the truth and is being a good LCD.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112376
> Signed-off-by: Lyude Paul <ly...@redhat.com>
Acked-by: Jani Nikula <jani.nik...@intel.com>
> ---
> drivers/gpu/drm/drm_dp_helper.c | 4 ++++
> drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 10 ++++++++--
> include/drm/drm_dp_helper.h | 8 ++++++++
> 3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 2c7870aef469..ec7061e3a99b 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -1155,6 +1155,10 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
> { OUI(0x00, 0x10, 0xfa), DEVICE_ID_ANY, false,
> BIT(DP_DPCD_QUIRK_NO_PSR) },
> /* CH7511 seems to leave SINK_COUNT zeroed */
> { OUI(0x00, 0x00, 0x00), DEVICE_ID('C', 'H', '7', '5', '1', '1'),
> false, BIT(DP_DPCD_QUIRK_NO_SINK_COUNT) },
> + /* Optional 4K AMOLED panel in the ThinkPad X1 Extreme 2nd Generation
> + * only supports DPCD backlight controls, despite advertising otherwise
> + */
> + { OUI(0xba, 0x41, 0x59), DEVICE_ID_ANY, false,
> BIT(DP_DPCD_QUIRK_FORCE_DPCD_BACKLIGHT) },
> };
>
> #undef OUI
> 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 87b59db9ffe3..3d61260b08ad 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -325,11 +325,17 @@ 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);
> + struct intel_dp *intel_dp =
> + enc_to_intel_dp(&intel_connector->encoder->base);
> + 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))
> + dev_priv->vbt.backlight.type !=
> + INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE &&
> + !drm_dp_has_quirk(&intel_dp->desc,
> + DP_DPCD_QUIRK_FORCE_DPCD_BACKLIGHT)))
> return -ENODEV;
>
> if (!intel_dp_aux_display_control_capable(intel_connector))
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 51ecb5112ef8..a444209cd54b 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1520,6 +1520,14 @@ enum drm_dp_quirk {
> * The driver should ignore SINK_COUNT during detection.
> */
> DP_DPCD_QUIRK_NO_SINK_COUNT,
> + /**
> + * @DP_DPCD_QUIRK_FORCE_DPCD_BACKLIGHT:
> + *
> + * The device is telling the truth when it says that it uses DPCD
> + * backlight controls, even if the system's firmware disagrees.
> + * The driver should honor the DPCD backlight capabilities advertised.
> + */
> + DP_DPCD_QUIRK_FORCE_DPCD_BACKLIGHT,
> };
>
> /**
--
Jani Nikula, Intel Open Source Graphics Center
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