mmc: core: Return 1 from mmc_regulator_set_vqmmc() if switch skipped

Adjust mmc_regulator_set_vqmmc() to return 1 if the voltage switch was
skipped because the regulator voltage was already correct. This allows
drivers to detect such condition and possibly skip various voltage
switching extras.
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20200416163649.336967-2-marex@denx.deSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/regulator.c

@@ -136,6 +136,8 @@ static int mmc_regulator_set_voltage_if_supported(struct regulator *regulator,
 						  int min_uV, int target_uV,
 						  int max_uV)
 {
+	int current_uV;
+
 	/*
 	 * Check if supported first to avoid errors since we may try several
 	 * signal levels during power up and don't want to show errors.
@@ -143,6 +145,14 @@ static int mmc_regulator_set_voltage_if_supported(struct regulator *regulator,
 	if (!regulator_is_supported_voltage(regulator, min_uV, max_uV))
 		return -EINVAL;
 
+	/*
+	 * The voltage is already set, no need to switch.
+	 * Return 1 to indicate that no switch happened.
+	 */
+	current_uV = regulator_get_voltage(regulator);
+	if (current_uV == target_uV)
+		return 1;
+
 	return regulator_set_voltage_triplet(regulator, min_uV, target_uV,
 					     max_uV);
 }
@@ -198,9 +208,10 @@ int mmc_regulator_set_vqmmc(struct mmc_host *mmc, struct mmc_ios *ios)
 		 * voltage in two steps and try to stay close to vmmc
 		 * with a 0.3V tolerance at first.
 		 */
-		if (!mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
-						min_uV, volt, max_uV))
-			return 0;
+		ret = mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
+							min_uV, volt, max_uV);
+		if (ret >= 0)
+			return ret;
 
 		return mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
 						2700000, volt, 3600000);