[Intel-gfx] [PATCH v2 11/15] drm/i915: Protect DSPARB registers with a spinlock

[ville.syrjala at linux.intel.com]

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

Each DSPARB register can house bits for two separate pipes, hence
we must protect the registers during reprogramming so that parallel
FIFO reconfigurations happening simultaneosly on multiple pipes won't
corrupt each others values.

We'll use a new spinlock for this instead of the wm_mutex since we'll
have to move the DSPARB programming to happen from the vblank evade
critical section, and we can't use mutexes in there.

v2: Document why we use a spinlock instead of a mutex (Maarten)

Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 1 +
 drivers/gpu/drm/i915/i915_drv.h | 3 +++
 drivers/gpu/drm/i915/intel_pm.c | 6 ++++++
 3 files changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 0fba4bb5655e..c98032e9112b 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -811,6 +811,7 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
 	spin_lock_init(&dev_priv->uncore.lock);
 	spin_lock_init(&dev_priv->mm.object_stat_lock);
 	spin_lock_init(&dev_priv->mmio_flip_lock);
+	spin_lock_init(&dev_priv->wm.dsparb_lock);
 	mutex_init(&dev_priv->sb_lock);
 	mutex_init(&dev_priv->modeset_restore_lock);
 	mutex_init(&dev_priv->av_mutex);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9d808b706824..75439e9a67f7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2169,6 +2169,9 @@ struct drm_i915_private {
 	} sagv_status;
 
 	struct {
+		/* protects DSPARB registers on pre-g4x/vlv/chv */
+		spinlock_t dsparb_lock;
+
 		/*
 		 * Raw watermark latency values:
 		 * in 0.1us units for WM0,
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 24d85a4e4ed3..9f25f2195a6a 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -1215,6 +1215,8 @@ static void vlv_pipe_set_fifo_size(struct intel_crtc *crtc)
 		      pipe_name(crtc->pipe), sprite0_start,
 		      sprite1_start, fifo_size);
 
+	spin_lock(&dev_priv->wm.dsparb_lock);
+
 	switch (crtc->pipe) {
 		uint32_t dsparb, dsparb2, dsparb3;
 	case PIPE_A:
@@ -1271,6 +1273,10 @@ static void vlv_pipe_set_fifo_size(struct intel_crtc *crtc)
 	default:
 		break;
 	}
+
+	POSTING_READ(DSPARB);
+
+	spin_unlock(&dev_priv->wm.dsparb_lock);
 }
 
 #undef VLV_FIFO
-- 
2.7.4