1 files changed, 117 insertions, 0 deletions

diff --git a/drivers/gpu/nvgpu/common/posix/rwsem.c b/drivers/gpu/nvgpu/common/posix/rwsem.c
new file mode 100644
index 00000000..7a696b75
--- /dev/null
+++ b/drivers/gpu/nvgpu/common/posix/rwsem.c
@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <nvgpu/bug.h>
+#include <nvgpu/rwsem.h>
+#include <nvgpu/timers.h>
+
+#include <nvgpu/posix/rwsem.h>
+
+void nvgpu_rwsem_init(struct nvgpu_rwsem *rwsem)
+{
+        memset(rwsem, 0, sizeof(*rwsem));
+
+        nvgpu_spinlock_init(&rwsem->lock);
+}
+
+/*
+ * Acquire.
+ */
+void nvgpu_rwsem_down_read(struct nvgpu_rwsem *rwsem)
+{
+        while (true) {
+                nvgpu_spinlock_acquire(&rwsem->lock);
+
+                /*
+                 * If there's a writer try again.
+                 */
+                if (rwsem->writers < 0) {
+                        nvgpu_spinlock_release(&rwsem->lock);
+                        nvgpu_msleep(10);
+                        continue;
+                }
+
+                /*
+                 * Otherwise decrement the read counter and return.
+                 */
+                rwsem->readers -= 1;
+                nvgpu_spinlock_release(&rwsem->lock);
+                return;
+        }
+}
+
+/*
+ * Release.
+ */
+void nvgpu_rwsem_up_read(struct nvgpu_rwsem *rwsem)
+{
+        nvgpu_spinlock_acquire(&rwsem->lock);
+        rwsem->readers += 1;
+
+        /*
+         * Can't be any writers if there was a reader. Also can't be
+         * a positive number of readers. The increments are always
+         * downward so if we have a positive number then there is a
+         * balancing bug.
+         */
+        BUG_ON(rwsem->writers < 0);
+        BUG_ON(rwsem->readers > 0);
+
+        nvgpu_spinlock_release(&rwsem->lock);
+}
+
+void nvgpu_rwsem_down_write(struct nvgpu_rwsem *rwsem)
+{
+        while (true) {
+                nvgpu_spinlock_acquire(&rwsem->lock);
+
+                /*
+                 * If there's a reader or a writer try again. Note: in this very
+                 * simple implementation it's possible for readers to
+                 * indefinitely starve writers.
+                 */
+                if (rwsem->writers < 0 || rwsem->readers < 0) {
+                        nvgpu_spinlock_release(&rwsem->lock);
+                        nvgpu_msleep(10);
+                        continue;
+                }
+
+                rwsem->writers -= 1;
+                nvgpu_spinlock_release(&rwsem->lock);
+                return;
+        }
+}
+
+void nvgpu_rwsem_up_write(struct nvgpu_rwsem *rwsem)
+{
+        nvgpu_spinlock_acquire(&rwsem->lock);
+        rwsem->writers += 1;
+
+        /*
+         * Writers can't be positive: that would be an unbalanced free. Readers
+         * must be zero - otherwise this writer should never have had access!
+         */
+        BUG_ON(rwsem->writers > 0);
+        BUG_ON(rwsem->readers != 0);
+
+        nvgpu_spinlock_release(&rwsem->lock);
+}