[U-Boot] [PATCH V2] mmc: introduce mmc_power_init

[Peng Fan]

In device tree, there is vmmc-supply property for SD/MMC.
Introduce mmc_power_init function to handle vmmc-supply.

mmc_power_init will first invoke board_mmc_power_init to
avoid break boards which already implement board_mmc_power_init.

If DM_MMC and DM_REGULATOR is defined, the regulator
will be enabled to power up the device.

Signed-off-by: Peng Fan <peng.fan at nxp.com>
Cc: Jaehoon Chung <jh80.chung at samsung.com>
---

V2:
 Change function prototype to static.
 Use puts to replace debug, when no vmmc-supply.

V1: Use a generic way to handle vmmc supply, but not let vendor driver
    to handle it.

The RFC patset thread:
http://lists.denx.de/pipermail/u-boot/2016-April/251019.html

 drivers/mmc/mmc.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 0312da9..320413a 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -15,6 +15,7 @@
 #include <errno.h>
 #include <mmc.h>
 #include <part.h>
+#include <power/regulator.h>
 #include <malloc.h>
 #include <memalign.h>
 #include <linux/list.h>
@@ -1582,6 +1583,31 @@ __weak void board_mmc_power_init(void)
 {
 }
 
+static int mmc_power_init(struct mmc *mmc)
+{
+	board_mmc_power_init();
+
+#if defined(CONFIG_DM_MMC) && defined(CONFIG_DM_REGULATOR) && \
+	!defined(CONFIG_SPL_BUILD)
+	struct udevice *vmmc_supply;
+	int ret;
+
+	ret = device_get_supply_regulator(mmc->dev, "vmmc-supply",
+					  &vmmc_supply);
+	if (ret) {
+		puts("No vmmc supply\n");
+		return 0;
+	}
+
+	ret = regulator_set_enable(vmmc_supply, true);
+	if (ret) {
+		puts("Error enabling VMMC supply\n");
+		return ret;
+	}
+#endif
+	return 0;
+}
+
 int mmc_start_init(struct mmc *mmc)
 {
 	bool no_card;
@@ -1606,7 +1632,9 @@ int mmc_start_init(struct mmc *mmc)
 #ifdef CONFIG_FSL_ESDHC_ADAPTER_IDENT
 	mmc_adapter_card_type_ident();
 #endif
-	board_mmc_power_init();
+	err = mmc_power_init(mmc);
+	if (err)
+		return err;
 
 #ifdef CONFIG_DM_MMC_OPS
 	/* The device has already been probed ready for use */
-- 
2.6.2