[v3.10][v3.11][v3.12][Regression][PATCH 1/1] Revert "Revert "drm/i915: revert eDP bpp clamping code changes""

[Joseph Salisbury]

BugLink: http://bugs.launchpad.net/bugs/1195483

This reverts commit 657445fe8660100ad174600ebfa61536392b7624.

Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Paulo Zanoni <przanoni at gmail.com>
Cc: David Airlie <airlied at linux.ie>
Cc: stable at vger.kernel.org


---
 drivers/gpu/drm/i915/intel_dp.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 26e162b..ce933ad 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -709,10 +709,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 
 	/* Walk through all bpp values. Luckily they're all nicely spaced with 2
 	 * bpc in between. */
-	bpp = pipe_config->pipe_bpp;
-	if (is_edp(intel_dp) && dev_priv->vbt.edp_bpp)
-		bpp = min_t(int, bpp, dev_priv->vbt.edp_bpp);
-
+	bpp = min_t(int, 8*3, pipe_config->pipe_bpp);
 	for (; bpp >= 6*3; bpp -= 2*3) {
 		mode_rate = intel_dp_link_required(adjusted_mode->clock, bpp);
 
@@ -763,6 +760,19 @@ found:
 			       &pipe_config->dp_m_n);
 
 	intel_dp_set_clock(encoder, pipe_config, intel_dp->link_bw);
+	/*
+	 * XXX: We have a strange regression where using the vbt edp bpp value
+	 * for the link bw computation results in black screens, the panel only
+	 * works when we do the computation at the usual 24bpp (but still
+	 * requires us to use 18bpp). Until that's fully debugged, stay
+	 * bug-for-bug compatible with the old code.
+	 */
+	if (is_edp(intel_dp) && dev_priv->vbt.edp_bpp) {
+		DRM_DEBUG_KMS("clamping display bpc (was %d) to eDP (%d)\n",
+			      bpp, dev_priv->vbt.edp_bpp);
+		bpp = min_t(int, bpp, dev_priv->vbt.edp_bpp);
+	}
+	pipe_config->pipe_bpp = bpp;
 
 	return true;
 }
-- 
1.7.9.5