mtd: rawnand: Add a helper to parse the gpio-cs DT property

New chips may feature a lot of CS because of their extended length. As
many controllers have been designed a decade ago, they usually only
feature just a couple. This does not mean that the entire range of
these chips cannot be accessed: it is just a matter of adding more
GPIO CS in the hardware design. A DT property has been added to
describe the CS array: cs-gpios.

Here is the code parsing it this new property, allocating what needs to
be, requesting the GPIOs and returning an array with the additional
available CS. The first entries of this array are left empty and are
reserved for native CS.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210526093242.183847-3-miquel.raynal@bootlin.com

2 files changed, 43 insertions, 0 deletions

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 22974a53077f..57a583149cc0 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -42,6 +42,7 @@
 #include <linux/io.h>
 #include <linux/mtd/partitions.h>
 #include <linux/of.h>
+#include <linux/of_gpio.h>
 #include <linux/gpio/consumer.h>
 
 #include "internals.h"
@@ -5249,6 +5250,44 @@ static int of_get_nand_secure_regions(struct nand_chip *chip)
 	return 0;
 }
 
+/**
+ * rawnand_dt_parse_gpio_cs - Parse the gpio-cs property of a controller
+ * @dev: Device that will be parsed. Also used for managed allocations.
+ * @cs_array: Array of GPIO desc pointers allocated on success
+ * @ncs_array: Number of entries in @cs_array updated on success.
+ * @return 0 on success, an error otherwise.
+ */
+int rawnand_dt_parse_gpio_cs(struct device *dev, struct gpio_desc ***cs_array,
+			     unsigned int *ncs_array)
+{
+	struct device_node *np = dev->of_node;
+	struct gpio_desc **descs;
+	int ndescs, i;
+
+	ndescs = of_gpio_named_count(np, "cs-gpios");
+	if (ndescs < 0) {
+		dev_dbg(dev, "No valid cs-gpios property\n");
+		return 0;
+	}
+
+	descs = devm_kcalloc(dev, ndescs, sizeof(*descs), GFP_KERNEL);
+	if (!descs)
+		return -ENOMEM;
+
+	for (i = 0; i < ndescs; i++) {
+		descs[i] = gpiod_get_index_optional(dev, "cs", i,
+						    GPIOD_OUT_HIGH);
+		if (IS_ERR(descs[i]))
+			return PTR_ERR(descs[i]);
+	}
+
+	*ncs_array = ndescs;
+	*cs_array = descs;
+
+	return 0;
+}
+EXPORT_SYMBOL(rawnand_dt_parse_gpio_cs);
+
 static int rawnand_dt_init(struct nand_chip *chip)
 {
 	struct nand_device *nand = mtd_to_nanddev(nand_to_mtd(chip));
diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
index d41d39360fff..b2f9dd3cbd69 100644
--- a/include/linux/mtd/rawnand.h
+++ b/include/linux/mtd/rawnand.h
@@ -1595,4 +1595,8 @@ static inline void *nand_get_data_buf(struct nand_chip *chip)
 	return chip->data_buf;
 }
 
+/* Parse the gpio-cs property */
+int rawnand_dt_parse_gpio_cs(struct device *dev, struct gpio_desc ***cs_array,
+			     unsigned int *ncs_array);
+
 #endif /* __LINUX_MTD_RAWNAND_H */