drm/i915: Introduce struct intel_wakeref

For controlling runtime pm of the GT and engines, we would like to have
a callback to do extra work the first time we wake up and the last time
we drop the wakeref. This first/last access needs serialisation and so
we encompass a mutex with the regular intel_wakeref_t tracker.

v2: Drop the _once naming and report the errors.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc; Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190424200717.1686-1-chris@chris-wilson.co.uk

1 files changed, 61 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_wakeref.c b/drivers/gpu/drm/i915/intel_wakeref.c
new file mode 100644
index 000000000000..1f94bc4ff9e4
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_wakeref.c
@@ -0,0 +1,61 @@
+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2019 Intel Corporation
+ */
+
+#include "intel_drv.h"
+#include "intel_wakeref.h"
+
+int __intel_wakeref_get_first(struct drm_i915_private *i915,
+			      struct intel_wakeref *wf,
+			      int (*fn)(struct intel_wakeref *wf))
+{
+	/*
+	 * Treat get/put as different subclasses, as we may need to run
+	 * the put callback from under the shrinker and do not want to
+	 * cross-contanimate that callback with any extra work performed
+	 * upon acquiring the wakeref.
+	 */
+	mutex_lock_nested(&wf->mutex, SINGLE_DEPTH_NESTING);
+	if (!atomic_read(&wf->count)) {
+		int err;
+
+		wf->wakeref = intel_runtime_pm_get(i915);
+
+		err = fn(wf);
+		if (unlikely(err)) {
+			intel_runtime_pm_put(i915, wf->wakeref);
+			mutex_unlock(&wf->mutex);
+			return err;
+		}
+
+		smp_mb__before_atomic(); /* release wf->count */
+	}
+	atomic_inc(&wf->count);
+	mutex_unlock(&wf->mutex);
+
+	return 0;
+}
+
+int __intel_wakeref_put_last(struct drm_i915_private *i915,
+			     struct intel_wakeref *wf,
+			     int (*fn)(struct intel_wakeref *wf))
+{
+	int err;
+
+	err = fn(wf);
+	if (likely(!err))
+		intel_runtime_pm_put(i915, wf->wakeref);
+	else
+		atomic_inc(&wf->count);
+	mutex_unlock(&wf->mutex);
+
+	return err;
+}
+
+void __intel_wakeref_init(struct intel_wakeref *wf, struct lock_class_key *key)
+{
+	__mutex_init(&wf->mutex, "wakeref", key);
+	atomic_set(&wf->count, 0);
+}