mmc: dw_mmc: Handle wp-gpios from device tree

On some SoCs (like exynos5250) you need to use an external GPIO for
write protect.  Add support for wp-gpios to the core dw_mmc driver
since it could be useful across multiple SoCs.

With this change I am able to make use of the write protect for the
external SD slot on exynos5250-snow.
Signed-off-by: Doug Anderson <dianders@chromium.org>
Acked-by: Seungwon Jeon <tgih.jun@samsung.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/dw_mmc.c

@@ -34,6 +34,7 @@
 #include <linux/regulator/consumer.h>
 #include <linux/workqueue.h>
 #include <linux/of.h>
+#include <linux/of_gpio.h>
 
 #include "dw_mmc.h"
 
@@ -75,6 +76,7 @@ struct idmac_desc {
  * @mmc: The mmc_host representing this slot.
  * @host: The MMC controller this slot is using.
  * @quirks: Slot-level quirks (DW_MCI_SLOT_QUIRK_XXX)
+ * @wp_gpio: If gpio_is_valid() we'll use this to read write protect.
  * @ctype: Card type for this slot.
  * @mrq: mmc_request currently being processed or waiting to be
  *	processed, or NULL when the slot is idle.
@@ -90,6 +92,7 @@ struct dw_mci_slot {
 	struct dw_mci		*host;
 
 	int			quirks;
+	int			wp_gpio;
 
 	u32			ctype;
 
@@ -838,6 +841,8 @@ static int dw_mci_get_ro(struct mmc_host *mmc)
 		read_only = 0;
 	else if (brd->get_ro)
 		read_only = brd->get_ro(slot->id);
+	else if (gpio_is_valid(slot->wp_gpio))
+		read_only = gpio_get_value(slot->wp_gpio);
 	else
 		read_only =
 			mci_readl(slot->host, WRTPRT) & (1 << slot->id) ? 1 : 0;
@@ -1832,6 +1837,29 @@ static u32 dw_mci_of_get_bus_wd(struct device *dev, u8 slot)
 			       " as 1\n");
 	return bus_wd;
 }
+
+/* find the write protect gpio for a given slot; or -1 if none specified */
+static int dw_mci_of_get_wp_gpio(struct device *dev, u8 slot)
+{
+	struct device_node *np = dw_mci_of_find_slot_node(dev, slot);
+	int gpio;
+
+	if (!np)
+		return -EINVAL;
+
+	gpio = of_get_named_gpio(np, "wp-gpios", 0);
+
+	/* Having a missing entry is valid; return silently */
+	if (!gpio_is_valid(gpio))
+		return -EINVAL;
+
+	if (devm_gpio_request(dev, gpio, "dw-mci-wp")) {
+		dev_warn(dev, "gpio [%d] request failed\n", gpio);
+		return -EINVAL;
+	}
+
+	return gpio;
+}
 #else /* CONFIG_OF */
 static int dw_mci_of_get_slot_quirks(struct device *dev, u8 slot)
 {
@@ -1845,6 +1873,10 @@ static struct device_node *dw_mci_of_find_slot_node(struct device *dev, u8 slot)
 {
 	return NULL;
 }
+static int dw_mci_of_get_wp_gpio(struct device *dev, u8 slot)
+{
+	return -EINVAL;
+}
 #endif /* CONFIG_OF */
 
 static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
@@ -1962,6 +1994,8 @@ static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
 	else
 		clear_bit(DW_MMC_CARD_PRESENT, &slot->flags);
 
+	slot->wp_gpio = dw_mci_of_get_wp_gpio(host->dev, slot->id);
+
 	mmc_add_host(mmc);
 
 #if defined(CONFIG_DEBUG_FS)