[PATCH v2 1/2] nvmem: core: deprecate reg_write callback and add reg_write_const

This callback used to take a mutable void * for no reason, which causes
the compiler to be unaware that the val buffer should never be modified
by the callback.

This was found while drafting the nvmem-provider Rust abstraction.

Signed-off-by: Link Mauve <[email protected]>
---
 drivers/nvmem/core.c           | 26 +++++++++++++++++---------
 drivers/nvmem/internals.h      |  1 +
 include/linux/nvmem-provider.h |  6 +++++-
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index e871181751f3..24c9e6f953c6 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -62,13 +62,20 @@ 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)
+			     const void *val, size_t bytes)
 {
 	int ret;
 
+	if (nvmem->reg_write_const) {
+		gpiod_set_value_cansleep(nvmem->wp_gpio, 0);
+		ret = nvmem->reg_write_const(nvmem->priv, offset, val, bytes);
+		gpiod_set_value_cansleep(nvmem->wp_gpio, 1);
+		return ret;
+	}
+
 	if (nvmem->reg_write) {
 		gpiod_set_value_cansleep(nvmem->wp_gpio, 0);
-		ret = nvmem->reg_write(nvmem->priv, offset, val, bytes);
+		ret = nvmem->reg_write(nvmem->priv, offset, (void *)val, bytes);
 		gpiod_set_value_cansleep(nvmem->wp_gpio, 1);
 		return ret;
 	}
@@ -264,7 +271,7 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
 
 	count = round_down(count, nvmem->word_size);
 
-	if (!nvmem->reg_write || nvmem->read_only)
+	if (!nvmem->reg_write || !nvmem->reg_write_const || nvmem->read_only)
 		return -EPERM;
 
 	rc = nvmem_reg_write(nvmem, pos, buf, count);
@@ -285,7 +292,7 @@ static umode_t nvmem_bin_attr_get_umode(struct nvmem_device *nvmem)
 	if (!nvmem->read_only)
 		mode |= 0200;
 
-	if (!nvmem->reg_write)
+	if (!nvmem->reg_write || !nvmem->reg_write_const)
 		mode &= ~0200;
 
 	if (!nvmem->reg_read)
@@ -321,13 +328,13 @@ static umode_t nvmem_attr_is_visible(struct kobject *kobj,
 	struct nvmem_device *nvmem = to_nvmem_device(dev);
 
 	/*
-	 * If the device has no .reg_write operation, do not allow
-	 * configuration as read-write.
+	 * If the device has no .reg_write or .reg_write_const operation, do
+	 * not allow configuration as read-write.
 	 * If the device is set as read-only by configuration, it
 	 * can be forced into read-write mode using the 'force_ro'
 	 * attribute.
 	 */
-	if (attr == &dev_attr_force_ro.attr && !nvmem->reg_write)
+	if (attr == &dev_attr_force_ro.attr && !nvmem->reg_write && !nvmem->reg_write_const)
 		return 0;	/* Attribute not visible */
 
 	return attr->mode;
@@ -905,7 +912,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	if (!config->dev)
 		return ERR_PTR(-EINVAL);
 
-	if (!config->reg_read && !config->reg_write)
+	if (!config->reg_read && !config->reg_write && !config->reg_write_const)
 		return ERR_PTR(-EINVAL);
 
 	nvmem = kzalloc_obj(*nvmem);
@@ -950,6 +957,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	nvmem->type = config->type;
 	nvmem->reg_read = config->reg_read;
 	nvmem->reg_write = config->reg_write;
+	nvmem->reg_write_const = config->reg_write_const;
 	nvmem->keepout = config->keepout;
 	nvmem->nkeepout = config->nkeepout;
 	if (config->of_node)
@@ -975,7 +983,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 		goto err_put_device;
 
 	nvmem->read_only = device_property_present(config->dev, "read-only") ||
-			   config->read_only || !nvmem->reg_write;
+			   config->read_only || !nvmem->reg_write || !nvmem->reg_write_const;
 
 #ifdef CONFIG_NVMEM_SYSFS
 	nvmem->dev.groups = nvmem_dev_groups;
diff --git a/drivers/nvmem/internals.h b/drivers/nvmem/internals.h
index 18fed57270e5..184711dfd6a6 100644
--- a/drivers/nvmem/internals.h
+++ b/drivers/nvmem/internals.h
@@ -29,6 +29,7 @@ struct nvmem_device {
 	unsigned int		nkeepout;
 	nvmem_reg_read_t	reg_read;
 	nvmem_reg_write_t	reg_write;
+	nvmem_reg_write_const_t	reg_write_const;
 	struct gpio_desc	*wp_gpio;
 	struct nvmem_layout	*layout;
 	void *priv;
diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index f3b13da78aac..c6e77ba1a8c1 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -20,6 +20,8 @@ typedef int (*nvmem_reg_read_t)(void *priv, unsigned int offset,
 				void *val, size_t bytes);
 typedef int (*nvmem_reg_write_t)(void *priv, unsigned int offset,
 				 void *val, size_t bytes);
+typedef int (*nvmem_reg_write_const_t)(void *priv, unsigned int offset,
+				       const void *val, size_t bytes);
 /* used for vendor specific post processing of cell data */
 typedef int (*nvmem_cell_post_process_t)(void *priv, const char *id, int index,
 					 unsigned int offset, void *buf,
@@ -93,7 +95,8 @@ struct nvmem_cell_info {
  * @root_only:	Device is accessibly to root only.
  * @of_node:	If given, this will be used instead of the parent's of_node.
  * @reg_read:	Callback to read data; return zero if successful.
- * @reg_write:	Callback to write data; return zero if successful.
+ * @reg_write:	**DEPRECATED** - please use reg_write_const instead.
+ * @reg_write_const:	Callback to write data; return zero if successful.
  * @size:	Device size.
  * @word_size:	Minimum read/write access granularity.
  * @stride:	Minimum read/write access stride.
@@ -128,6 +131,7 @@ struct nvmem_config {
 	struct device_node	*of_node;
 	nvmem_reg_read_t	reg_read;
 	nvmem_reg_write_t	reg_write;
+	nvmem_reg_write_const_t	reg_write_const;
 	int	size;
 	int	word_size;
 	int	stride;
-- 
2.55.0