On Fri, 22 Nov 2019, Lyude Paul <lyude@xxxxxxxxxx> wrote: > For eDP panels, it appears it's expected that so long as the panel is in > DPCD control mode that the brightness value is never set to 0. Instead, > if the desired effect is to set the panel's backlight to 0 we're > expected to simply turn off the backlight through the > DP_EDP_DISPLAY_CONTROL_REGISTER. > > We already do the latter correctly in intel_dp_aux_disable_backlight(). > But, we make the mistake of writing the DPCD registers in the wrong > order when enabling the backlight in intel_dp_aux_enable_backlight() > since we currently enable the backlight through > DP_EDP_DISPLAY_CONTROL_REGISTER before writing the brightness level. On > the X1 Extreme 2nd Generation, this appears to have the potential of > confusing the panel in such a way that further attempts to set the > brightness don't actually change the backlight as expected and leave it > off. Presumably, this happens because the incorrect register writing > order briefly leaves the panel with DPCD mode enabled and a 0 brightness > level set. > > So, reverse the order we write the DPCD registers when enabling the > panel backlight so that we write the brightness value first, and enable > the backlight second. This fix appears to be the final bit needed to get > the backlight on the ThinkPad X1 Extreme 2nd Generation's AMOLED screen > working. > > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx> Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx> > --- > drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > 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 0bf8772bc7bb..87b59db9ffe3 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c > @@ -205,8 +205,9 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st > } > } > > + intel_dp_aux_set_backlight(conn_state, > + connector->panel.backlight.level); > set_aux_backlight_enable(intel_dp, true); > - intel_dp_aux_set_backlight(conn_state, connector->panel.backlight.level); > } > > static void intel_dp_aux_disable_backlight(const struct drm_connector_state *old_conn_state) -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
