gpu: nvgpu: Userspace POSIX support

Add support for compiling nvgpu in a POSIX compliant userspace.
This code adds all of the necessary abstraction interfaces (mostly
stubbed) to enabled extremely limited and basic functionality in
nvgpu.

The goal of this code is to facilitate unit testing of the nvgpu
common core. By doing this in userspace it is much easier to write
tests that rely on very particular states within nvgpu since a user
can very precisely control the state of nvgpu.

JIRA NVGPU-525

Change-Id: I30e95016df14997d951075777e0585f912dc5960
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1683914
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

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);
+}