mmc: sdhci: Export sdhci_start_signal_voltage_switch() in sdhci.c

Export sdhci_start_signal_voltage_switch() from sdhci.c.
Thus vendor sdhci driver can implement its own signal voltage
switch routine.
Signed-off-by: NHu Ziji <huziji@marvell.com>
Signed-off-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: NAdrian Hunter <adrian.hunter@intel.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci.c

@@ -1853,8 +1853,8 @@ static void sdhci_enable_sdio_irq(struct mmc_host *mmc, int enable)
 		pm_runtime_put_noidle(host->mmc->parent);
 }
 
-static int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
-					     struct mmc_ios *ios)
+int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
+				      struct mmc_ios *ios)
 {
 	struct sdhci_host *host = mmc_priv(mmc);
 	u16 ctrl;
@@ -1946,6 +1946,7 @@ static int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
 		return 0;
 	}
 }
+EXPORT_SYMBOL_GPL(sdhci_start_signal_voltage_switch);
 
 static int sdhci_card_busy(struct mmc_host *mmc)
 {

drivers/mmc/host/sdhci.h

@@ -704,6 +704,8 @@ void sdhci_reset(struct sdhci_host *host, u8 mask);
 void sdhci_set_uhs_signaling(struct sdhci_host *host, unsigned timing);
 int sdhci_execute_tuning(struct mmc_host *mmc, u32 opcode);
 void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios);
+int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
+				      struct mmc_ios *ios);
 
 #ifdef CONFIG_PM
 int sdhci_suspend_host(struct sdhci_host *host);