[Bug 97965] [BSW] External HDMI monitor suddenly shows solid color when playing Youtube video at 1080p [fifo underrun]

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97965

--- Comment #25 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Yu Kang Ku from comment #24)
> For the pipe B experiment, I'm running into some hurdles that will take some
> more time to fix.
> 
> Meanwhile, I did the following experiment which might indicate that the
> problem is isolated to pipe C.  I closed the lid so that the primary display
> would go away while the external HDMI display would continue with the video
> playback.  This is basically dock mode.  Yet, the problem is still
> reproducible.  The output of intel_watermark is here:
> https://bugs.freedesktop.org/attachment.cgi?id=127107

That's not a bit too different since it's gone and enabled PM5 and DDR DVFS. So
you should limit it to PM2 to make sure we're doing apples to apples
comparison.
Eg.:
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -946,7 +946,7 @@ static void vlv_setup_wm_latency(struct drm_device *dev)

        dev_priv->wm.max_level = VLV_WM_LEVEL_PM2;

-       if (IS_CHERRYVIEW(dev_priv)) {
+       if (0 && IS_CHERRYVIEW(dev_priv)) {
                dev_priv->wm.pri_latency[VLV_WM_LEVEL_PM5] = 12;
                dev_priv->wm.pri_latency[VLV_WM_LEVEL_DDR_DVFS] = 33;


Another thing you could try is enable trickle feed. That shouldn't change much
though as it's essentially just always forcing the watermarks to 8 or something
like that. But worth a shot anyway I suppose:

--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -1070,7 +1070,7 @@ static void vlv_init_display_clock_gating(struct
drm_i915_private *dev_priv)
        /*
         * Disable trickle feed and enable pnd deadline calculation
         */
-       I915_WRITE(MI_ARB_VLV, MI_ARB_DISPLAY_TRICKLE_FEED_DISABLE);
+       I915_WRITE(MI_ARB_VLV, 0);
        I915_WRITE(CBR1_VLV, 0);

        WARN_ON(dev_priv->rawclk_freq == 0);

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