regulator: core: Fix off_on_delay handling

The jiffies-based off_on_delay implementation has a couple of problems
that cause it to sometimes not actually delay for the required time:

 (1) If, for example, the off_on_delay time is equivalent to one jiffy,
     and the ->last_off_jiffy is set just before a new jiffy starts,
     then _regulator_do_enable() does not wait at all since it checks
     using time_before().

 (2) When jiffies overflows, the value of "remaining" becomes higher
     than "max_delay" and the code simply proceeds without waiting.

Fix these problems by changing it to use ktime_t instead.

[Note that since jiffies doesn't start at zero but at INITIAL_JIFFIES
 ("-5 minutes"), (2) above also led to the code not delaying if
 the first regulator_enable() is called when the ->last_off_jiffy is not
 initialised, such as for regulators with ->constraints->boot_on set.
 It's not clear to me if this was intended or not, but I've preserved
 this behaviour explicitly with the check for a non-zero ->last_off.]

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20210423114524.26414-1-vincent.whitchurch@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -1443,7 +1443,7 @@ static int set_machine_constraints(struct regulator_dev *rdev)
 		if (rdev->constraints->always_on)
 			rdev->use_count++;
 	} else if (rdev->desc->off_on_delay) {
-		rdev->last_off_jiffy = jiffies;
+		rdev->last_off = ktime_get();
 	}
 
 	print_constraints(rdev);
@@ -2488,29 +2488,15 @@ static int _regulator_do_enable(struct regulator_dev *rdev)
 
 	trace_regulator_enable(rdev_get_name(rdev));
 
-	if (rdev->desc->off_on_delay) {
+	if (rdev->desc->off_on_delay && rdev->last_off) {
 		/* if needed, keep a distance of off_on_delay from last time
 		 * this regulator was disabled.
 		 */
-		unsigned long start_jiffy = jiffies;
-		unsigned long intended, max_delay, remaining;
-
-		max_delay = usecs_to_jiffies(rdev->desc->off_on_delay);
-		intended = rdev->last_off_jiffy + max_delay;
-
-		if (time_before(start_jiffy, intended)) {
-			/* calc remaining jiffies to deal with one-time
-			 * timer wrapping.
-			 * in case of multiple timer wrapping, either it can be
-			 * detected by out-of-range remaining, or it cannot be
-			 * detected and we get a penalty of
-			 * _regulator_enable_delay().
-			 */
-			remaining = intended - start_jiffy;
-			if (remaining <= max_delay)
-				_regulator_enable_delay(
-						jiffies_to_usecs(remaining));
-		}
+		ktime_t end = ktime_add_us(rdev->last_off, rdev->desc->off_on_delay);
+		s64 remaining = ktime_us_delta(end, ktime_get());
+
+		if (remaining > 0)
+			_regulator_enable_delay(remaining);
 	}
 
 	if (rdev->ena_pin) {
@@ -2740,11 +2726,8 @@ static int _regulator_do_disable(struct regulator_dev *rdev)
 			return ret;
 	}
 
-	/* cares about last_off_jiffy only if off_on_delay is required by
-	 * device.
-	 */
 	if (rdev->desc->off_on_delay)
-		rdev->last_off_jiffy = jiffies;
+		rdev->last_off = ktime_get();
 
 	trace_regulator_disable_complete(rdev_get_name(rdev));
 

include/linux/regulator/driver.h

@@ -476,7 +476,7 @@ struct regulator_dev {
 	unsigned int is_switch:1;
 
 	/* time when this regulator was disabled last time */
-	unsigned long last_off_jiffy;
+	ktime_t last_off;
 };
 
 struct regulator_dev *