It is useful to be able to wait on pending rendering without grabbing
the struct_mutex. We can do this by using the i915_gem_active_get_rcu()
primitive to acquire a reference to the pending request without
requiring struct_mutex, just the RCU read lock, and then call
i915_wait_request().
v2: Rebase onto new i915_gem_active_get_unlocked() semantics that take
the RCU read lock on behalf of the caller.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem_request.h | 40 +++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
index 6002adc43523..15495d1e48e8 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.h
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -569,6 +569,46 @@ i915_gem_active_wait(const struct i915_gem_active *active, struct mutex *mutex)
}
/**
+ * i915_gem_active_wait_unlocked - waits until the request is completed
+ * @active - the active request on which to wait
+ * @interruptible - whether the wait can be woken by a userspace signal
+ * @timeout - how long to wait at most
+ * @rps - userspace client to charge for a waitboost
+ *
+ * i915_gem_active_wait_unlocked() waits until the request is completed before
+ * returning, without requiring any locks to be held. Note that it does not
+ * retire any requests before returning.
+ *
+ * This function relies on RCU in order to acquire the reference to the active
+ * request without holding any locks. See __i915_gem_active_get_rcu() for the
+ * glory details on how that is managed. Once the reference is acquired, we
+ * can then wait upon the request, and afterwards release our reference,
+ * free of any locking.
+ *
+ * This function wraps i915_wait_request(), see it for the full details on
+ * the arguments.
+ *
+ * Returns 0 if successful, or a negative error code.
+ */
+static inline int
+i915_gem_active_wait_unlocked(const struct i915_gem_active *active,
+ bool interruptible,
+ s64 *timeout,
+ struct intel_rps_client *rps)
+{
+ struct drm_i915_gem_request *request;
+ int ret = 0;
+
+ request = i915_gem_active_get_unlocked(active);
+ if (request) {
+ ret = i915_wait_request(request, interruptible, timeout, rps);
+ i915_gem_request_put(request);
+ }
+
+ return ret;
+}
+
+/**
* i915_gem_active_retire - waits until the request is retired
* @active - the active request on which to wait
*
--
2.8.1
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