regulator: core: correct convergence check in regulator_set_voltage()

The logic in regulator_set_voltage() which checks for a non-convergence
condition on a stepped regulator is flawed.

regulator_set_voltage() checks if the error in target voltage has increased
or decreased, and returns -EWOULDBLOCK if the error has not decreased
enough. The correct non-convergence condition is:

new_delta - delta > -rdev->constraints->max_uV_step

or equivalently:

delta - new_delta < rdev->constraints->max_uV_step

But the currently used condition is:

new_delta - delta > rdev->constraints->max_uV_step

Which may cause an infinite loop if the voltage error doesn't converge.

Fix this by correcting the convergence condition.

Suggested-by: Jon Hunter <[email protected]>
Fixes: d511206 ("regulator: core: repeat voltage setting request for stepped regulators")
Signed-off-by: Romain Gantois <[email protected]>
Link: https://patch.msgid.link/[email protected]
Tested-by: Jon Hunter <[email protected]>
Reviewed-by: Jon Hunter <[email protected]>
Signed-off-by: Mark Brown <[email protected]>

Author: rgantois

drivers/regulator/core.c

@@ -3884,7 +3884,7 @@ static int regulator_set_voltage_unlocked(struct regulator *regulator,
 			new_delta = ret;
 
 			/* check that voltage is converging quickly enough */
-			if (new_delta - delta > rdev->constraints->max_uV_step) {
+			if (delta - new_delta < rdev->constraints->max_uV_step) {
 				ret = -EWOULDBLOCK;
 				goto out;
 			}