drm/i915: Prefer checking the wakeref itself rather than the counter

The counter goes to zero at the start of the parking cycle, but the
wakeref itself is held until the end. Likewise, the counter becomes one
at the end of the unparking, but the wakeref is taken first. If we check
the wakeref instead of the counter, we include the unpark/unparking time
as intel_wakeref_is_active(), and do not spuriously declare inactive if
we fail to park (i.e. the parking and wakeref drop is postponed).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190503115225.30831-2-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/intel_wakeref.c b/drivers/gpu/drm/i915/intel_wakeref.c
index 1f94bc4ff9e4e2f584bd940c2abdeadbf102d147..91196d9612bbf2f4a8d089b94c03d384b1d75341 100644 (file)
--- a/drivers/gpu/drm/i915/intel_wakeref.c
+++ b/drivers/gpu/drm/i915/intel_wakeref.c
@@ -7,6 +7,19 @@
 #include "intel_drv.h"
 #include "intel_wakeref.h"
 
+static void rpm_get(struct drm_i915_private *i915, struct intel_wakeref *wf)
+{
+       wf->wakeref = intel_runtime_pm_get(i915);
+}
+
+static void rpm_put(struct drm_i915_private *i915, struct intel_wakeref *wf)
+{
+       intel_wakeref_t wakeref = fetch_and_zero(&wf->wakeref);
+
+       intel_runtime_pm_put(i915, wakeref);
+       GEM_BUG_ON(!wakeref);
+}
+
 int __intel_wakeref_get_first(struct drm_i915_private *i915,
                              struct intel_wakeref *wf,
                              int (*fn)(struct intel_wakeref *wf))
@@ -21,11 +34,11 @@ int __intel_wakeref_get_first(struct drm_i915_private *i915,
        if (!atomic_read(&wf->count)) {
                int err;
 
-               wf->wakeref = intel_runtime_pm_get(i915);
+               rpm_get(i915, wf);
 
                err = fn(wf);
                if (unlikely(err)) {
-                       intel_runtime_pm_put(i915, wf->wakeref);
+                       rpm_put(i915, wf);
                        mutex_unlock(&wf->mutex);
                        return err;
                }
@@ -46,7 +59,7 @@ int __intel_wakeref_put_last(struct drm_i915_private *i915,
 
        err = fn(wf);
        if (likely(!err))
-               intel_runtime_pm_put(i915, wf->wakeref);
+               rpm_put(i915, wf);
        else
                atomic_inc(&wf->count);
        mutex_unlock(&wf->mutex);
@@ -58,4 +71,5 @@ void __intel_wakeref_init(struct intel_wakeref *wf, struct lock_class_key *key)
 {
        __mutex_init(&wf->mutex, "wakeref", key);
        atomic_set(&wf->count, 0);
+       wf->wakeref = 0;
 }

diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
index a979d638344bb0e057226aec3a3d6a1827dd1e4a..db742291211cfc7625db020eeaa7209f2e30092b 100644 (file)
--- a/drivers/gpu/drm/i915/intel_wakeref.h
+++ b/drivers/gpu/drm/i915/intel_wakeref.h
@@ -127,7 +127,7 @@ intel_wakeref_unlock(struct intel_wakeref *wf)
 static inline bool
 intel_wakeref_active(struct intel_wakeref *wf)
 {
-       return atomic_read(&wf->count);
+       return READ_ONCE(wf->wakeref);
 }
 
 #endif /* INTEL_WAKEREF_H */