We do have to continue the investigation on the link training side, but since 76711 is a critical I'm completely in favor of this workaround for now.
I just tested and it worked very well here, so:
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
On Wed, May 14, 2014 at 6:02 AM, Jani Nikula <jani.nikula@xxxxxxxxx> wrote:
There are certain BDW high res eDP machines that regressed due to
commit 38aecea0ccbb909d635619cba22f1891e589b434
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
Date: Mon Mar 3 11:18:10 2014 +0100
drm/i915: reverse dp link param selection, prefer fast over wide again
The commit lead to 2 lanes at 5.4 Gbps being used instead of 4 lanes at
2.7 Gbps on the affected machines. Link training succeeded for both, but
the screen remained blank with the former config. Further investigation
showed that 4 lanes at 5.4 Gbps worked also.
The root cause for the blank screen using 2 lanes remains unknown, but
apparently the driver for a certain other operating system by default
uses the max available lanes. Follow suit on Broadwell eDP, for at least
until we figure out what is going on.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76711
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_dp.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 9f67b724dc28..6eaefca0048d 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -849,7 +849,12 @@ intel_dp_compute_config(struct intel_encoder *encoder,
bpp = dev_priv->vbt.edp_bpp;
}
- if (dev_priv->vbt.edp_lanes) {
+ if (IS_BROADWELL(dev)) {
+ /* Yes, it's an ugly hack. */
+ min_lane_count = max_lane_count;
+ DRM_DEBUG_KMS("forcing lane count to max (%u) on BDW\n",
+ min_lane_count);
+ } else if (dev_priv->vbt.edp_lanes) {
min_lane_count = min(dev_priv->vbt.edp_lanes,
max_lane_count);
DRM_DEBUG_KMS("using min %u lanes per VBT\n",
--
1.9.1
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Rodrigo Vivi
Blog: http://blog.vivi.eng.br
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