nvmem: add support for the write-protect pin

The write-protect pin handling looks like a standard property that
could benefit other users if available in the core nvmem framework.

Instead of modifying all the memory drivers to check this pin, make
the NVMEM subsystem check if the write-protect GPIO being passed
through the nvmem_config or defined in the device tree and pull it
low whenever writing to the memory.

There was a suggestion for introducing the gpiodesc from pdata, but
as pdata is already removed it could be replaced by adding it to
nvmem_config.

Reference: https://lists.96boards.org/pipermail/dev/2018-August/001056.html

Signed-off-by: Khouloud Touil <ktouil@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

3 files changed, 22 insertions, 2 deletions

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 9f1ee9c766ec..3e1c94c4eee8 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/nvmem-consumer.h>
 #include <linux/nvmem-provider.h>
+#include <linux/gpio/consumer.h>
 #include <linux/of.h>
 #include <linux/slab.h>
 #include "nvmem.h"
@@ -54,8 +55,14 @@ static int nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
 static int nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
 			   void *val, size_t bytes)
 {
-	if (nvmem->reg_write)
-		return nvmem->reg_write(nvmem->priv, offset, val, bytes);
+	int ret;
+
+	if (nvmem->reg_write) {
+		gpiod_set_value_cansleep(nvmem->wp_gpio, 0);
+		ret = nvmem->reg_write(nvmem->priv, offset, val, bytes);
+		gpiod_set_value_cansleep(nvmem->wp_gpio, 1);
+		return ret;
+	}
 
 	return -EINVAL;
 }
@@ -338,6 +345,14 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 		kfree(nvmem);
 		return ERR_PTR(rval);
 	}
+	if (config->wp_gpio)
+		nvmem->wp_gpio = config->wp_gpio;
+	else
+		nvmem->wp_gpio = gpiod_get_optional(config->dev, "wp",
+						    GPIOD_OUT_HIGH);
+	if (IS_ERR(nvmem->wp_gpio))
+		return PTR_ERR(nvmem->wp_gpio);
+
 
 	kref_init(&nvmem->refcnt);
 	INIT_LIST_HEAD(&nvmem->cells);
diff --git a/drivers/nvmem/nvmem.h b/drivers/nvmem/nvmem.h
index eb8ed7121fa3..be0d66d75c8a 100644
--- a/drivers/nvmem/nvmem.h
+++ b/drivers/nvmem/nvmem.h
@@ -9,6 +9,7 @@
 #include <linux/list.h>
 #include <linux/nvmem-consumer.h>
 #include <linux/nvmem-provider.h>
+#include <linux/gpio/consumer.h>
 
 struct nvmem_device {
 	struct module		*owner;
@@ -26,6 +27,7 @@ struct nvmem_device {
 	struct list_head	cells;
 	nvmem_reg_read_t	reg_read;
 	nvmem_reg_write_t	reg_write;
+	struct gpio_desc	*wp_gpio;
 	void *priv;
 };
 
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index fe051323be0a..6d6f8e5d24c9 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -11,6 +11,7 @@
 
 #include <linux/err.h>
 #include <linux/errno.h>
+#include <linux/gpio/consumer.h>
 
 struct nvmem_device;
 struct nvmem_cell_info;
@@ -45,6 +46,7 @@ enum nvmem_type {
  * @word_size:	Minimum read/write access granularity.
  * @stride:	Minimum read/write access stride.
  * @priv:	User context passed to read/write callbacks.
+ * @wp-gpio:   Write protect pin
  *
  * Note: A default "nvmem<id>" name will be assigned to the device if
  * no name is specified in its configuration. In such case "<id>" is
@@ -58,6 +60,7 @@ struct nvmem_config {
 	const char		*name;
 	int			id;
 	struct module		*owner;
+	struct gpio_desc	*wp_gpio;
 	const struct nvmem_cell_info	*cells;
 	int			ncells;
 	enum nvmem_type		type;