Messages in this thread | | | Subject | Re: [v2] drm/i915: Assume 100% brightness when not in DPCD control mode | From | Perr Yuan <> | Date | Mon, 23 Dec 2019 02:17:54 -0500 |
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On 12/3/19 5:42 PM, Lyude Paul wrote: > Currently we always determine the initial panel brightness level by > simply reading the value from DP_EDP_BACKLIGHT_BRIGHTNESS_MSB/LSB. This > seems wrong though, because if the panel is not currently in DPCD > control mode there's not really any reason why there would be any > brightness value programmed in the first place. > > This appears to be the case on the Lenovo ThinkPad X1 Extreme 2nd > Generation, where the default value in these registers is always 0 on > boot despite the fact the panel runs at max brightness by default. > Getting the initial brightness value correct here is important as well, > since the panel on this laptop doesn't behave well if it's ever put into > DPCD control mode while the brightness level is programmed to 0. > > So, let's fix this by checking what the current backlight control mode > is before reading the brightness level. If it's in DPCD control mode, we > return the programmed brightness level. Otherwise we assume 100% > brightness and return the highest possible brightness level. This also > prevents us from accidentally programming a brightness level of 0. > > This is one of the many fixes that gets backlight controls working on > the ThinkPad X1 Extreme 2nd Generation with optional 4K AMOLED screen. > > Changes since v1: > * s/DP_EDP_DISPLAY_CONTROL_REGISTER/DP_EDP_BACKLIGHT_MODE_SET_REGISTER/ > - Jani > > Signed-off-by: Lyude Paul <lyude@redhat.com> > --- > .../drm/i915/display/intel_dp_aux_backlight.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > 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 fad470553cf9..4d467e7d29eb 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > @@ -59,8 +59,25 @@ static u32 intel_dp_aux_get_backlight(struct intel_connector *connector) > { > struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base); > u8 read_val[2] = { 0x0 }; > + u8 mode_reg; > u16 level = 0; > > + if (drm_dp_dpcd_readb(&intel_dp->aux, > + DP_EDP_BACKLIGHT_MODE_SET_REGISTER, > + &mode_reg) != 1) { > + DRM_DEBUG_KMS("Failed to read the DPCD register 0x%x\n", > + DP_EDP_BACKLIGHT_MODE_SET_REGISTER); > + return 0; > + } > + > + /* > + * If we're not in DPCD control mode yet, the programmed brightness > + * value is meaningless and we should assume max brightness > + */ > + if ((mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) != > + DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) > + return connector->panel.backlight.max; > + > if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, > &read_val, sizeof(read_val)) < 0) { > DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n", >
Tested-by:Perry Yuan <pyuan@redhat.com>
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