drm/i915: Warn if we run out of FIFO space for a mode

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index baaaeaac7f21..132314e2bf21 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2745,8 +2745,14 @@ static unsigned long intel_calculate_wm(unsigned long clock_in_khz,
         /* Don't promote wm_size to unsigned... */
         if (wm_size > (long)wm->max_wm)
                 wm_size = wm->max_wm;
-        if (wm_size <= 0)
+        if (wm_size <= 0) {
                 wm_size = wm->default_wm;
+                DRM_ERROR("Insufficient FIFO for plane, expect flickering:"
+                          " entries required = %ld, available = %lu.\n",
+                          entries_required + wm->guard_size,
+                          wm->fifo_size);
+        }
+
         return wm_size;
 }