tree 90dbb7b3b922569986f1e5f538df7f9b713254ca
parent 82922da39190199260a726d7081a8ea4873e5fd6
author Lyude <cpaul@redhat.com> 1460730335 -0400
committer Daniel Vetter <daniel.vetter@ffwll.ch> 1461343944 +0200

drm/dp_helper: Perform throw-away read before actual read in drm_dp_dpcd_read()

This is part of a patch series to migrate all of the workarounds for
commonly seen behavior from bad sinks in intel_dp_dpcd_read_wake() to drm's
DP helper.

Some sinks will just return garbage for the first aux tranaction they
receive when coming out of sleep mode, so we need to perform an additional
read before the actual read to workaround this.

			    Changes since v5
- If the throwaway read in drm_dp_dpcd_read() fails, return the error
  from that instead of continuing. This follows the same logic we do in
  drm_dp_dpcd_access() (e.g. the error from the first transaction may
  differ from the errors that proceeding attempts might return).

Signed-off-by: Lyude <cpaul@redhat.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460730335-5012-1-git-send-email-cpaul@redhat.com