[PATCH 4/9] drm/i915/dsb: Stop with the RMW

[Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>]

From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>

We don't want to keep random bits set in DSB_CTRL. Stop the
harmful RMW.

Also flip the reverse & around to appease my ocd.

Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/display/intel_dsb.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
index 5bb4ac1610a5..8b357b35c41f 100644
--- a/drivers/gpu/drm/i915/display/intel_dsb.c
+++ b/drivers/gpu/drm/i915/display/intel_dsb.c
@@ -40,7 +40,7 @@ static inline bool is_dsb_busy(struct intel_dsb *dsb)
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 	enum pipe pipe = crtc->pipe;
 
-	return DSB_STATUS & intel_de_read(dev_priv, DSB_CTRL(pipe, dsb->id));
+	return intel_de_read(dev_priv, DSB_CTRL(pipe, dsb->id)) & DSB_STATUS;
 }
 
 static inline bool intel_dsb_enable_engine(struct intel_dsb *dsb)
@@ -48,18 +48,15 @@ static inline bool intel_dsb_enable_engine(struct intel_dsb *dsb)
 	struct intel_crtc *crtc = container_of(dsb, typeof(*crtc), dsb);
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 	enum pipe pipe = crtc->pipe;
-	u32 dsb_ctrl;
 
-	dsb_ctrl = intel_de_read(dev_priv, DSB_CTRL(pipe, dsb->id));
-	if (DSB_STATUS & dsb_ctrl) {
+	if (is_dsb_busy(dsb)) {
 		DRM_ERROR("DSB engine is busy.\n");
 		return false;
 	}
 
-	dsb_ctrl |= DSB_ENABLE;
-	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), dsb_ctrl);
-
+	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), DSB_ENABLE);
 	intel_de_posting_read(dev_priv, DSB_CTRL(pipe, dsb->id));
+
 	return true;
 }
 
@@ -68,18 +65,15 @@ static inline bool intel_dsb_disable_engine(struct intel_dsb *dsb)
 	struct intel_crtc *crtc = container_of(dsb, typeof(*crtc), dsb);
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 	enum pipe pipe = crtc->pipe;
-	u32 dsb_ctrl;
 
-	dsb_ctrl = intel_de_read(dev_priv, DSB_CTRL(pipe, dsb->id));
-	if (DSB_STATUS & dsb_ctrl) {
+	if (is_dsb_busy(dsb)) {
 		DRM_DEBUG_KMS("DSB engine is busy.\n");
 		return false;
 	}
 
-	dsb_ctrl &= ~DSB_ENABLE;
-	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), dsb_ctrl);
-
+	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
 	intel_de_posting_read(dev_priv, DSB_CTRL(pipe, dsb->id));
+
 	return true;
 }
 
-- 
2.24.1

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