drm/i915: Disable FIFO underrun reporting around IBX transcoder B workaround

Doing the IBX transcoder B workaround causes underruns on
pipe/transcoder A. Just hide them by disabling underrun reporting for
pipe A around the workaround.

It might be possible to avoid the underruns by moving the workaround
to be applied only when enabling pipe A. But I was too lazy to try it
right now, and the current method has been proven to work, so didn't
want to change it too hastily.

Note that this can re-enable underrun reporting on pipe A if was
already disabled due to a previous actual underrun. But that's OK, we
may just get a second underrun report if another real underron occurrs
on pipe A.

v2: Note that pipe A underruns can get re-enabled due to this (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> (v1)
Link: http://patchwork.freedesktop.org/patch/msgid/1446225802-11180-1-git-send-email-ville.syrjala@linux.intel.com

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index c42b636c2087..267e6cb76c4a 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -1464,12 +1464,23 @@ static void intel_disable_sdvo(struct intel_encoder *encoder)
 	 * matching DP port to be enabled on transcoder A.
 	 */
 	if (HAS_PCH_IBX(dev_priv) && crtc->pipe == PIPE_B) {
+		/*
+		 * We get CPU/PCH FIFO underruns on the other pipe when
+		 * doing the workaround. Sweep them under the rug.
+		 */
+		intel_set_cpu_fifo_underrun_reporting(dev_priv, PIPE_A, false);
+		intel_set_pch_fifo_underrun_reporting(dev_priv, PIPE_A, false);
+
 		temp &= ~SDVO_PIPE_B_SELECT;
 		temp |= SDVO_ENABLE;
 		intel_sdvo_write_sdvox(intel_sdvo, temp);
 
 		temp &= ~SDVO_ENABLE;
 		intel_sdvo_write_sdvox(intel_sdvo, temp);
+
+		intel_wait_for_vblank_if_active(dev_priv->dev, PIPE_A);
+		intel_set_cpu_fifo_underrun_reporting(dev_priv, PIPE_A, true);
+		intel_set_pch_fifo_underrun_reporting(dev_priv, PIPE_A, true);
 	}
 }