[Bug 59841] [IVB cpu eDP] panel is broken due to 657445fe86 (eDP bpp clamping)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=59841

--- Comment #198 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to jkp from comment #197)
> Well, regarding comment 194, my understanding is that my patch (the quirk or
> module param to ignore bpp from EDP) should be a no-op in CSM mode, as bpp
> in CSM mode is reported as 24 and the bpp before querying EDP is 24 as well,
> so ignoring EDP bpp shouldn't matter.

True. The way it fails just seems strange. Please do try it again, maybe
without another display attached.

For another data point, once you find a working setup in CSM first, please
apply the patch below on top. The idea is to ensure our dithering code works
for you, all else being equal. There are some other subtle differences between
UEFI and CSM too.

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 5614365..0315747 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -828,6 +828,9 @@ intel_dp_compute_config(struct intel_encoder *encoder,
         bpp = min_t(int, bpp, dev_priv->vbt.edp_bpp);
     }

+    bpp = 18;
+    DRM_DEBUG_KMS("clamping bpp for eDP panel to %i\n", bpp);
+
     for (; bpp >= 6*3; bpp -= 2*3) {
         mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
                            bpp);

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