[Bug 73567] [915 Haswell ULT Asus UX302LA/LG] eDP bpp clamping results in blank screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=73567

--- Comment #15 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to comment #13)
> Daniel, 
> 
> I'm already running drm-intel-nightly which includes that commit.
> That particular hack does indeed run (see attached dmesg log at the
> beginning) but the panel is still blank. I saw the same hack at
> intel_dp_get_config, but in my machine intel_dp_get_config does not get
> called at all.
> 
> The culprit is clamping bpp from 24 to 18 bpp at intel_dp_compute_config.
> When the bpp clamping code is disabled and the panel runs at 24 bpp there
> are no more blank screen issues. 

Please try this on drm-intel-nightly, and report what the debug says:

diff --git a/drivers/gpu/drm/i915/intel_ddi.c
b/drivers/gpu/drm/i915/intel_ddi.c
index 74749c6..dbc5a16 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1491,6 +1491,10 @@ void intel_ddi_get_config(struct intel_encoder *encoder,
                break;
        }

+       DRM_DEBUG_KMS("encoder type %d, pipe_bpp %d, vbt.edp_bpp %d, ddi ctl
%08x\n",
+                     encoder->type, pipe_config->pipe_bpp,
+                     dev_priv->vbt.edp_bpp, temp);
+
        if (encoder->type == INTEL_OUTPUT_EDP && dev_priv->vbt.edp_bpp &&
            pipe_config->pipe_bpp > dev_priv->vbt.edp_bpp) {
                /*

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