We only need a very lightweight mechanism here as the locking is only
used for co-ordinating a bitfield.

v2: Move the cheap unlikely tests into the caller

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtien <joonas.lahti...@linux.intel.com>

Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
[After some kerneldoc fixes, which I hope Daniel explains better,
Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch>]
---
 drivers/gpu/drm/i915/i915_drv.h          |  2 +-
 drivers/gpu/drm/i915/i915_gem.c          |  2 +-
 drivers/gpu/drm/i915/intel_drv.h         | 29 +++++++++++++++---
 drivers/gpu/drm/i915/intel_frontbuffer.c | 52 ++++++++++++++------------------
 4 files changed, 50 insertions(+), 35 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7ba99057c317..b26f5b1f466b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1669,7 +1669,7 @@ struct intel_pipe_crc {
 };
 
 struct i915_frontbuffer_tracking {
-       struct mutex lock;
+       spinlock_t lock;
 
        /*
         * Tracking bits for delayed frontbuffer flushing du to gpu activity or
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 72935f5c6ed1..5d57258d96cd 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4446,7 +4446,7 @@ i915_gem_load_init(struct drm_device *dev)
 
        dev_priv->mm.interruptible = true;
 
-       mutex_init(&dev_priv->fb_tracking.lock);
+       spin_lock_init(&dev_priv->fb_tracking.lock);
 }
 
 void i915_gem_load_cleanup(struct drm_device *dev)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index e74d851868c5..01056ce8d461 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1135,8 +1135,6 @@ void intel_ddi_set_vc_payload_alloc(struct drm_crtc 
*crtc, bool state);
 uint32_t ddi_signal_levels(struct intel_dp *intel_dp);
 
 /* intel_frontbuffer.c */
-void intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
-                            enum fb_op_origin origin);
 void intel_frontbuffer_flip_prepare(struct drm_device *dev,
                                    unsigned frontbuffer_bits);
 void intel_frontbuffer_flip_complete(struct drm_device *dev,
@@ -1147,8 +1145,31 @@ unsigned int intel_fb_align_height(struct drm_device 
*dev,
                                   unsigned int height,
                                   uint32_t pixel_format,
                                   uint64_t fb_format_modifier);
-void intel_fb_obj_flush(struct drm_i915_gem_object *obj, bool retire,
-                       enum fb_op_origin origin);
+
+void __intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
+                              enum fb_op_origin origin);
+static inline void intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
+                                          enum fb_op_origin origin)
+{
+       if (!obj->frontbuffer_bits)
+               return;
+
+       __intel_fb_obj_invalidate(obj, origin);
+}
+
+void __intel_fb_obj_flush(struct drm_i915_gem_object *obj,
+                         bool retire,
+                         enum fb_op_origin origin);
+static inline void intel_fb_obj_flush(struct drm_i915_gem_object *obj,
+                                     bool retire,
+                                     enum fb_op_origin origin)
+{
+       if (!obj->frontbuffer_bits)
+               return;
+
+       __intel_fb_obj_flush(obj, retire, origin);
+}
+
 u32 intel_fb_stride_alignment(const struct drm_i915_private *dev_priv,
                              uint64_t fb_modifier, uint32_t pixel_format);
 
diff --git a/drivers/gpu/drm/i915/intel_frontbuffer.c 
b/drivers/gpu/drm/i915/intel_frontbuffer.c
index ac85357010b4..939d0e8cf63d 100644
--- a/drivers/gpu/drm/i915/intel_frontbuffer.c
+++ b/drivers/gpu/drm/i915/intel_frontbuffer.c
@@ -76,24 +76,19 @@
  * until the rendering completes or a flip on this frontbuffer plane is
  * scheduled.
  */
-void intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
-                            enum fb_op_origin origin)
+void __intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
+                              enum fb_op_origin origin)
 {
        struct drm_device *dev = obj->base.dev;
        struct drm_i915_private *dev_priv = to_i915(dev);
 
        WARN_ON(!mutex_is_locked(&dev->struct_mutex));
 
-       if (!obj->frontbuffer_bits)
-               return;
-
        if (origin == ORIGIN_CS) {
-               mutex_lock(&dev_priv->fb_tracking.lock);
-               dev_priv->fb_tracking.busy_bits
-                       |= obj->frontbuffer_bits;
-               dev_priv->fb_tracking.flip_bits
-                       &= ~obj->frontbuffer_bits;
-               mutex_unlock(&dev_priv->fb_tracking.lock);
+               spin_lock(&dev_priv->fb_tracking.lock);
+               dev_priv->fb_tracking.busy_bits |= obj->frontbuffer_bits;
+               dev_priv->fb_tracking.flip_bits &= ~obj->frontbuffer_bits;
+               spin_unlock(&dev_priv->fb_tracking.lock);
        }
 
        intel_psr_invalidate(dev, obj->frontbuffer_bits);
@@ -120,9 +115,9 @@ static void intel_frontbuffer_flush(struct drm_device *dev,
        struct drm_i915_private *dev_priv = to_i915(dev);
 
        /* Delay flushing when rings are still busy.*/
-       mutex_lock(&dev_priv->fb_tracking.lock);
+       spin_lock(&dev_priv->fb_tracking.lock);
        frontbuffer_bits &= ~dev_priv->fb_tracking.busy_bits;
-       mutex_unlock(&dev_priv->fb_tracking.lock);
+       spin_unlock(&dev_priv->fb_tracking.lock);
 
        if (!frontbuffer_bits)
                return;
@@ -142,8 +137,9 @@ static void intel_frontbuffer_flush(struct drm_device *dev,
  * completed and frontbuffer caching can be started again. If @retire is true
  * then any delayed flushes will be unblocked.
  */
-void intel_fb_obj_flush(struct drm_i915_gem_object *obj,
-                       bool retire, enum fb_op_origin origin)
+void __intel_fb_obj_flush(struct drm_i915_gem_object *obj,
+                         bool retire,
+                         enum fb_op_origin origin)
 {
        struct drm_device *dev = obj->base.dev;
        struct drm_i915_private *dev_priv = to_i915(dev);
@@ -151,21 +147,18 @@ void intel_fb_obj_flush(struct drm_i915_gem_object *obj,
 
        WARN_ON(!mutex_is_locked(&dev->struct_mutex));
 
-       if (!obj->frontbuffer_bits)
-               return;
-
        frontbuffer_bits = obj->frontbuffer_bits;
 
        if (retire) {
-               mutex_lock(&dev_priv->fb_tracking.lock);
+               spin_lock(&dev_priv->fb_tracking.lock);
                /* Filter out new bits since rendering started. */
                frontbuffer_bits &= dev_priv->fb_tracking.busy_bits;
-
                dev_priv->fb_tracking.busy_bits &= ~frontbuffer_bits;
-               mutex_unlock(&dev_priv->fb_tracking.lock);
+               spin_unlock(&dev_priv->fb_tracking.lock);
        }
 
-       intel_frontbuffer_flush(dev, frontbuffer_bits, origin);
+       if (frontbuffer_bits)
+               intel_frontbuffer_flush(dev, frontbuffer_bits, origin);
 }
 
 /**
@@ -185,11 +178,11 @@ void intel_frontbuffer_flip_prepare(struct drm_device 
*dev,
 {
        struct drm_i915_private *dev_priv = to_i915(dev);
 
-       mutex_lock(&dev_priv->fb_tracking.lock);
+       spin_lock(&dev_priv->fb_tracking.lock);
        dev_priv->fb_tracking.flip_bits |= frontbuffer_bits;
        /* Remove stale busy bits due to the old buffer. */
        dev_priv->fb_tracking.busy_bits &= ~frontbuffer_bits;
-       mutex_unlock(&dev_priv->fb_tracking.lock);
+       spin_unlock(&dev_priv->fb_tracking.lock);
 
        intel_psr_single_frame_update(dev, frontbuffer_bits);
 }
@@ -209,13 +202,14 @@ void intel_frontbuffer_flip_complete(struct drm_device 
*dev,
 {
        struct drm_i915_private *dev_priv = to_i915(dev);
 
-       mutex_lock(&dev_priv->fb_tracking.lock);
+       spin_lock(&dev_priv->fb_tracking.lock);
        /* Mask any cancelled flips. */
        frontbuffer_bits &= dev_priv->fb_tracking.flip_bits;
        dev_priv->fb_tracking.flip_bits &= ~frontbuffer_bits;
-       mutex_unlock(&dev_priv->fb_tracking.lock);
+       spin_unlock(&dev_priv->fb_tracking.lock);
 
-       intel_frontbuffer_flush(dev, frontbuffer_bits, ORIGIN_FLIP);
+       if (frontbuffer_bits)
+               intel_frontbuffer_flush(dev, frontbuffer_bits, ORIGIN_FLIP);
 }
 
 /**
@@ -234,10 +228,10 @@ void intel_frontbuffer_flip(struct drm_device *dev,
 {
        struct drm_i915_private *dev_priv = to_i915(dev);
 
-       mutex_lock(&dev_priv->fb_tracking.lock);
+       spin_lock(&dev_priv->fb_tracking.lock);
        /* Remove stale busy bits due to the old buffer. */
        dev_priv->fb_tracking.busy_bits &= ~frontbuffer_bits;
-       mutex_unlock(&dev_priv->fb_tracking.lock);
+       spin_unlock(&dev_priv->fb_tracking.lock);
 
        intel_frontbuffer_flush(dev, frontbuffer_bits, ORIGIN_FLIP);
 }
-- 
2.8.1

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