drm/i915: reference counted forcewake

Provide a reference count to track the forcewake state of the GPU and
give a safe mechanism for userspace to wake the GT. This also potentially
saves a UC read if the GT is known to be awake already.

The reference count is atomic, but the register access and hardware wake
sequence is protected by struct_mutex.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 7 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 083644ef8f31..bafb387dd416 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -709,6 +709,8 @@ typedef struct drm_i915_private {
         struct intel_fbdev *fbdev;
 
         struct drm_property *broadcast_rgb_property;
+
+        atomic_t forcewake_count;
 } drm_i915_private_t;
 
 enum i915_cache_level {
@@ -1329,8 +1331,8 @@ extern void intel_display_print_error_state(struct seq_file *m,
  * must be set to prevent GT core from power down and stale values being
  * returned.
  */
-void __gen6_gt_force_wake_get(struct drm_i915_private *dev_priv);
-void __gen6_gt_force_wake_put(struct drm_i915_private *dev_priv);
+void gen6_gt_force_wake_get(struct drm_i915_private *dev_priv);
+void gen6_gt_force_wake_put(struct drm_i915_private *dev_priv);
 void __gen6_gt_wait_for_fifo(struct drm_i915_private *dev_priv);
 
 /* We give fast paths for the really cool registers */
@@ -1343,15 +1345,16 @@ void __gen6_gt_wait_for_fifo(struct drm_i915_private *dev_priv);
 static inline u##x i915_read##x(struct drm_i915_private *dev_priv, u32 reg) { \
         u##x val = 0; \
         if (NEEDS_FORCE_WAKE((dev_priv), (reg))) { \
-                __gen6_gt_force_wake_get(dev_priv); \
+                gen6_gt_force_wake_get(dev_priv); \
                 val = read##y(dev_priv->regs + reg); \
-                __gen6_gt_force_wake_put(dev_priv); \
+                gen6_gt_force_wake_put(dev_priv); \
         } else { \
                 val = read##y(dev_priv->regs + reg); \
         } \
         trace_i915_reg_rw(false, reg, val, sizeof(val)); \
         return val; \
 }
+
 __i915_read(8, b)
 __i915_read(16, w)
 __i915_read(32, l)