mtd: rawnand: Provide helper for polling GPIO R/B pin

Each controller driver having access to NAND R/B pin over GPIO would
have to reimplement the polling loop otherwise.
Suggested-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/nand_base.c

@@ -45,6 +45,7 @@
 #include <linux/io.h>
 #include <linux/mtd/partitions.h>
 #include <linux/of.h>
+#include <linux/gpio/consumer.h>
 
 #include "internals.h"
 
@@ -531,6 +532,36 @@ int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms)
 };
 EXPORT_SYMBOL_GPL(nand_soft_waitrdy);
 
+/**
+ * nand_gpio_waitrdy - Poll R/B GPIO pin until ready
+ * @chip: NAND chip structure
+ * @gpiod: GPIO descriptor of R/B pin
+ * @timeout_ms: Timeout in ms
+ *
+ * Poll the R/B GPIO pin until it becomes ready. If that does not happen
+ * whitin the specified timeout, -ETIMEDOUT is returned.
+ *
+ * This helper is intended to be used when the controller has access to the
+ * NAND R/B pin over GPIO.
+ *
+ * Return 0 if the R/B pin indicates chip is ready, a negative error otherwise.
+ */
+int nand_gpio_waitrdy(struct nand_chip *chip, struct gpio_desc *gpiod,
+		      unsigned long timeout_ms)
+{
+	/* Wait until R/B pin indicates chip is ready or timeout occurs */
+	timeout_ms = jiffies + msecs_to_jiffies(timeout_ms);
+	do {
+		if (gpiod_get_value_cansleep(gpiod))
+			return 0;
+
+		cond_resched();
+	} while	(time_before(jiffies, timeout_ms));
+
+	return gpiod_get_value_cansleep(gpiod) ? 0 : -ETIMEDOUT;
+};
+EXPORT_SYMBOL_GPL(nand_gpio_waitrdy);
+
 /**
  * panic_nand_get_device - [GENERIC] Get chip for selected access
  * @chip: the nand chip descriptor

include/linux/mtd/rawnand.h

@@ -1346,4 +1346,8 @@ void nand_release(struct nand_chip *chip);
  */
 int nand_soft_waitrdy(struct nand_chip *chip, unsigned long timeout_ms);
 
+struct gpio_desc;
+int nand_gpio_waitrdy(struct nand_chip *chip, struct gpio_desc *gpiod,
+		      unsigned long timeout_ms);
+
 #endif /* __LINUX_MTD_RAWNAND_H */