drm/i915: handle FIFO oversubsription correctly
If you're pushing a plane hard (i.e. you need most or all of the FIFO
entries just to cover your frame refresh latency), the watermark level
may end up being negative. So fix up the signed vs. unsigned math in
the calculation function to handle this correctly, giving all available
FIFO entries to such a configuration.
Reported-by: Eric Anholt <eric@anholt.net>
Tested-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3fa0d63..890f710 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1674,7 +1674,7 @@
int pixel_size,
unsigned long latency_ns)
{
- unsigned long entries_required, wm_size;
+ long entries_required, wm_size;
entries_required = (clock_in_khz * pixel_size * latency_ns) / 1000000;
entries_required /= wm->cacheline_size;
@@ -1685,9 +1685,10 @@
DRM_DEBUG("FIFO watermark level: %d\n", wm_size);
- if (wm_size > wm->max_wm)
+ /* 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;
return wm_size;
}