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Subject[PATCH] regulator: core: Reduce busy-wait looping
Date
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>
---
drivers/regulator/core.c | 38 +++++++++++++++++++++++++++++++++-----
1 file changed, 33 insertions(+), 5 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 4eefcc3..4e18884 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1566,11 +1566,39 @@ 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));
--
1.8.4


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