[PATCH v0] nvmem: core: Export nvmem cell info to userspace

[Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>]

From: Shiraz Hashim <shashim@xxxxxxxxxxxxxx>

Existing nvmem framework export full register space
as nvmem binary, but not exporting child node of nvmem
which is nvmem cell. Kernel can read the specific cell
by using nvmem_cell_read but userspace don't have such
provision.

Add framework to export nvmem cell as well, So
userspace can use it directly.

Signed-off-by: Shiraz Hashim <shashim@xxxxxxxxxxxxxx>
Signed-off-by: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>
Co-developed-by: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index f24008b..e4b6160 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -47,6 +47,7 @@ struct nvmem_cell {
 	int			nbits;
 	struct device_node	*np;
 	struct nvmem_device	*nvmem;
+	struct bin_attribute	attr;
 	struct list_head	node;
 };
 
@@ -99,6 +100,27 @@ static ssize_t type_show(struct device *dev,
 	return sprintf(buf, "%s\n", nvmem_type_str[nvmem->type]);
 }
 
+static ssize_t bin_attr_nvmem_cell_read(struct file *filp, struct kobject *kobj,
+				    struct bin_attribute *attr,
+				    char *buf, loff_t pos, size_t count)
+{
+	struct nvmem_cell *cell;
+	size_t len;
+	u8 *data;
+
+	if (attr->private)
+		cell = attr->private;
+	else
+		return -EINVAL;
+
+	data = nvmem_cell_read(cell, &len);
+
+	len = (len > count) ? count : len;
+	memcpy(buf, data, len);
+
+	return len;
+}
+
 static DEVICE_ATTR_RO(type);
 
 static struct attribute *nvmem_attrs[] = {
@@ -324,6 +346,7 @@ static void nvmem_cell_drop(struct nvmem_cell *cell)
 {
 	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_REMOVE, cell);
 	mutex_lock(&nvmem_mutex);
+	device_remove_bin_file(&cell->nvmem->dev, &cell->attr);
 	list_del(&cell->node);
 	mutex_unlock(&nvmem_mutex);
 	of_node_put(cell->np);
@@ -341,8 +364,24 @@ static void nvmem_device_remove_all_cells(const struct nvmem_device *nvmem)
 
 static void nvmem_cell_add(struct nvmem_cell *cell)
 {
+	int rval;
+	struct bin_attribute *nvmem_cell_attr = &cell->attr;
+
 	mutex_lock(&nvmem_mutex);
 	list_add_tail(&cell->node, &cell->nvmem->cells);
+
+	/* add attr for this cell */
+	nvmem_cell_attr->attr.name = cell->name;
+	nvmem_cell_attr->attr.mode = 0400;
+	nvmem_cell_attr->private = cell;
+	nvmem_cell_attr->size = cell->bytes;
+	nvmem_cell_attr->read = bin_attr_nvmem_cell_read;
+	rval = device_create_bin_file(&cell->nvmem->dev, nvmem_cell_attr);
+	if (rval) {
+		dev_err(&cell->nvmem->dev,
+			"Failed to create cell binary file %d\n", rval);
+	}
+
 	mutex_unlock(&nvmem_mutex);
 	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_ADD, cell);
 }
-- 
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