regulator: core: Reduce busy-wait looping

Keep busy-wait looping to a minimum while waiting for a regulator to
ramp-up to the target voltage. This follows the guidelines set forth
in Documentation/timers/timers-howto.txt and assumes that regulators
are never enabled in atomic context.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index ad154247bb906d446546f9cba469ef960c2be77f..5075ed1e94a6e63d22644bfc989e606e8f52d860 100644 (file)
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1740,11 +1740,39 @@ static int _regulator_do_enable(struct regulator_dev *rdev)
         * together.  */
        trace_regulator_enable_delay(rdev_get_name(rdev));
 
-       if (delay >= 1000) {
-               mdelay(delay / 1000);
-               udelay(delay % 1000);
-       } else if (delay) {
-               udelay(delay);
+       /*
+        * Delay for the requested amount of time as per the guidelines in:
+        *
+        *     Documentation/timers/timers-howto.txt
+        *
+        * The assumption here is that regulators will never be enabled in
+        * atomic context and therefore sleeping functions can be used.
+        */
+       if (delay) {
+               unsigned int ms = delay / 1000;
+               unsigned int us = delay % 1000;
+
+               if (ms > 0) {
+                       /*
+                        * For small enough values, handle super-millisecond
+                        * delays in the usleep_range() call below.
+                        */
+                       if (ms < 20)
+                               us += ms * 1000;
+                       else
+                               msleep(ms);
+               }
+
+               /*
+                * Give the scheduler some room to coalesce with any other
+                * wakeup sources. For delays shorter than 10 us, don't even
+                * bother setting up high-resolution timers and just busy-
+                * loop.
+                */
+               if (us >= 10)
+                       usleep_range(us, us + 100);
+               else
+                       udelay(us);
        }
 
        trace_regulator_enable_complete(rdev_get_name(rdev));