[Intel-gfx] [PATCH] drm/i915/vlv: Fix off-by-1 error in calculating num_levels.

[Maarten Lankhorst]

num_levels should be level+1, not level, else num_levels - 1 becomes
negative. This resulted in bogus watermarks being written to the first
255 levels like below:

[drm] Setting FIFO watermarks - C: plane=0, cursor=0, sprite0=0, sprite1=0, SR: plane=0, cursor=0 level=255 cxsr=0
[drm:chv_set_memory_dvfs [i915]] *ERROR* timed out waiting for Punit DDR DVFS request
[drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe C FIFO underrun
[drm:chv_set_memory_dvfs [i915]] *ERROR* timed out waiting for Punit DDR DVFS request

Testcase: kms_atomic_transition
Fixes: 262cd2e154c2 ("drm/i915: CHV DDR DVFS support and another watermark rewrite")
Cc: stable at vger.kernel.org
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
---
Urgent fix for watermark support. This is definitely a pre-requisite for this series.
With this I've noticed that patch "[RFC 3/8] drm/i915/vlv: Move fifo_size from
intel_plane_wm_parameters to vlv_wm_state" introduces a regression with invalid FIFO split.

I need to find out what's going wrong in that patch before this series can be applied.

 drivers/gpu/drm/i915/intel_pm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 376c60b98515..8defdcc54529 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -1148,7 +1148,7 @@ static void vlv_compute_wm(struct intel_crtc *crtc)
 			}
 		}
 
-		wm_state->num_levels = level;
+		wm_state->num_levels = level + 1;
 
 		if (!wm_state->cxsr)
 			continue;
-- 
2.7.4