Reviewed-by: Lyude Paul lyude@redhat.com

On Wed, 2019-08-28 at 13:20 +0300, Ville Syrjala wrote:

From: Ville Syrjälä ville.syrjala@linux.intel.com

My attempt at allowing MST to use the higher color depths has regressed some configurations. Apparently people have setups where all MST streams will fit into the DP link with 8bpc but won't fit with higher color depths.

What we really should be doing is reducing the bpc for all the streams on the same link until they start to fit. But that requires a bit more work, so in the meantime let's revert back closer to the old behavior and limit MST to at most 8bpc.

Cc: stable@vger.kernel.org Cc: Lyude Paul lyude@redhat.com Cc: Geoffrey Bennett gmux22@gmail.com Fixes: f1477219869c ("drm/i915: Remove the 8bpc shackles from DP MST") Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111505 Signed-off-by: Ville Syrjälä ville.syrjala@linux.intel.com

---

drivers/gpu/drm/i915/display/intel_dp_mst.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c index 2c5ac3dd647f..6df240a01b8c 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c @@ -128,7 +128,15 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder, limits.max_lane_count = intel_dp_max_lane_count(intel_dp); limits.min_bpp = intel_dp_min_bpp(pipe_config);

• limits.max_bpp = pipe_config->pipe_bpp;

• /*

• * FIXME: If all the streams can't fit into the link with
  

• * their current pipe_bpp we should reduce pipe_bpp across
  

• * the board until things start to fit. Until then we
  

• * limit to <= 8bpc since that's what was hardcoded for all
  

• * MST streams previously. This hack should be removed once
  

• * we have the proper retry logic in place.
  

• */
  

• limits.max_bpp = min(pipe_config->pipe_bpp, 24);

intel_dp_adjust_compliance_config(intel_dp, pipe_config, &limits);