[PATCH 4/6] drm/i915: Deal with cpp==8 for g4x watermarks

[Ville Syrjala <ville.syrjala@linux.intel.com>]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Docs tell us that on g4x we have to compute the SR watermarks
using 4 bytes per pixel. I'm going to assume that only applies
to 1 and 2 byte per pixel formats, and not 8 byte per pixel
formats. That seems like a recipe for an insufficient watermark
which could lead to underruns. Use the maximum of the two numbers
instead.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index d10c62d3f10c..87244d8215a7 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -1116,6 +1116,8 @@ static u16 g4x_compute_wm(const struct intel_crtc_state *crtc_state,
 	if (!intel_wm_plane_visible(crtc_state, plane_state))
 		return 0;
 
+	cpp = plane_state->base.fb->format->cpp[0];
+
 	/*
 	 * Not 100% sure which way ELK should go here as the
 	 * spec only says CL/CTG should assume 32bpp and BW
@@ -1129,9 +1131,7 @@ static u16 g4x_compute_wm(const struct intel_crtc_state *crtc_state,
 	 */
 	if (IS_GM45(dev_priv) && plane->id == PLANE_PRIMARY &&
 	    level != G4X_WM_LEVEL_NORMAL)
-		cpp = 4;
-	else
-		cpp = plane_state->base.fb->format->cpp[0];
+		cpp = max(cpp, 4u);
 
 	clock = adjusted_mode->crtc_clock;
 	htotal = adjusted_mode->crtc_htotal;
-- 
2.21.0

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