gpu: nvgpu: Abstraction for *sleep, *delay

Add abstractions for the following:

  msleep()
  udelay()
  usleep_range()

These functions are only a subset of the available Linux delay and sleep
functions but this seems to be what we use and what is actually useful
for driver development.

Bug 1799159
Jira NVGPU-16

Change-Id: I1a25b66314f365432f2f0a5ff1b3a0a5689fc047
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/1309087
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Seema Khowala <seemaj@nvidia.com>
Reviewed-by: David Martinez Nieto <dmartineznie@nvidia.com>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>

drivers/gpu/nvgpu/common/linux/timers.c

@@ -15,6 +15,7 @@
  */
 
 #include <linux/jiffies.h>
+#include <linux/delay.h>
 
 #include <nvgpu/timers.h>
 
@@ -175,3 +176,54 @@ int nvgpu_timeout_peek_expired(struct nvgpu_timeout *timeout)
 	else
 		return time_after(jiffies, (unsigned long)timeout->time);
 }
+
+/**
+ * nvgpu_udelay - Delay for some number of microseconds.
+ *
+ * @usecs - Microseconds to wait for.
+ *
+ * Wait for at least @usecs microseconds. This is not guaranteed to be perfectly
+ * accurate. This is normally backed by a busy-loop so this means waits should
+ * be kept short, below 100us. If longer delays are necessary then
+ * nvgpu_msleep() should be preferred.
+ *
+ * Alternatively, on some platforms, nvgpu_usleep_range() is usable. This
+ * function will attempt to not use a busy-loop.
+ */
+void nvgpu_udelay(unsigned int usecs)
+{
+	udelay(usecs);
+}
+
+/**
+ * nvgpu_usleep_range - Sleep for a range of microseconds.
+ *
+ * @min_us - Minimum wait time.
+ * @max_us - Maximum wait time.
+ *
+ * Wait for some number of microseconds between @min_us and @max_us. This,
+ * unlike nvgpu_udelay(), will attempt to sleep for the passed number of
+ * microseconds instead of busy looping. Not all platforms support this,
+ * and in that case this reduces to nvgpu_udelay(min_us).
+ *
+ * Linux note: this is not safe to use in atomic context. If you are in
+ * atomic context you must use nvgpu_udelay().
+ */
+void nvgpu_usleep_range(unsigned int min_us, unsigned int max_us)
+{
+	usleep_range(min_us, max_us);
+}
+
+/**
+ * nvgpu_msleep - Sleep for some milliseconds.
+ *
+ * @msecs - Sleep for at least this many milliseconds.
+ *
+ * Sleep for at least @msecs of milliseconds. For small @msecs (less than 20 ms
+ * or so) the sleep will be significantly longer due to scheduling overhead and
+ * mechanics.
+ */
+void nvgpu_msleep(unsigned int msecs)
+{
+	msleep(msecs);
+}