mmc: core: Add mmc_power_cycle

Add mmc_power_cycle which can be used to power cycle for instance
SD-cards.

Signed-off-by: Johan Rudholm <johan.rudholm@stericsson.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Wei WANG <wei_wang@realsil.com.cn>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/core.c

@@ -1470,6 +1470,14 @@ void mmc_power_off(struct mmc_host *host)
 	mmc_host_clk_release(host);
 }
 
+void mmc_power_cycle(struct mmc_host *host)
+{
+	mmc_power_off(host);
+	/* Wait at least 1 ms according to SD spec */
+	mmc_delay(1);
+	mmc_power_up(host);
+}
+
 /*
  * Cleanup when the last reference to the bus operator is dropped.
  */

drivers/mmc/core/core.h

@@ -45,6 +45,7 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage,
 void mmc_set_timing(struct mmc_host *host, unsigned int timing);
 void mmc_set_driver_type(struct mmc_host *host, unsigned int drv_type);
 void mmc_power_off(struct mmc_host *host);
+void mmc_power_cycle(struct mmc_host *host);
 
 static inline void mmc_delay(unsigned int ms)
 {