nvmem: ensure sysfs writes handle write-protect pin

Commit 2a127da4 ("nvmem: add support for the write-protect pin")
added support for handling write-protect pins to the nvmem core, and
Commit 1c89074b ("eeprom: at24: remove the write-protect pin support")
retrofitted the at24 driver to use this support.

These changes broke write() on the nvmem sysfs attribute for eeproms
which utilize a write-protect pin, as the write callback invokes the
nvmem device's reg_write callback directly which no longer handles
changing the state of the write-protect pin.

Change the read and write callbacks for the sysfs attribute to invoke
nvmme_reg_read/nvmem_reg_write helpers which handle this, rather than
calling reg_read/reg_write directly.

Fixes: 2a127da4 ("nvmem: add support for the write-protect pin")
Signed-off-by: Michael Auchter <michael.auchter@ni.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200511145042.31223-3-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -66,6 +66,30 @@ static LIST_HEAD(nvmem_lookup_list);
 
 static BLOCKING_NOTIFIER_HEAD(nvmem_notifier);
 
+static int nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
+			  void *val, size_t bytes)
+{
+	if (nvmem->reg_read)
+		return nvmem->reg_read(nvmem->priv, offset, val, bytes);
+
+	return -EINVAL;
+}
+
+static int nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
+			   void *val, size_t 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;
+}
+
 #ifdef CONFIG_NVMEM_SYSFS
 static const char * const nvmem_type_str[] = {
 	[NVMEM_TYPE_UNKNOWN] = "Unknown",
@@ -122,7 +146,7 @@ static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
 	if (!nvmem->reg_read)
 		return -EPERM;
 
-	rc = nvmem->reg_read(nvmem->priv, pos, buf, count);
+	rc = nvmem_reg_read(nvmem, pos, buf, count);
 
 	if (rc)
 		return rc;
@@ -159,7 +183,7 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
 	if (!nvmem->reg_write)
 		return -EPERM;
 
-	rc = nvmem->reg_write(nvmem->priv, pos, buf, count);
+	rc = nvmem_reg_write(nvmem, pos, buf, count);
 
 	if (rc)
 		return rc;
@@ -287,30 +311,6 @@ static void nvmem_sysfs_remove_compat(struct nvmem_device *nvmem,
 
 #endif /* CONFIG_NVMEM_SYSFS */
 
-static int nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
-			  void *val, size_t bytes)
-{
-	if (nvmem->reg_read)
-		return nvmem->reg_read(nvmem->priv, offset, val, bytes);
-
-	return -EINVAL;
-}
-
-static int nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
-			   void *val, size_t 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;
-}
-
 static void nvmem_release(struct device *dev)
 {
 	struct nvmem_device *nvmem = to_nvmem_device(dev);