regmap: Provide access information via debugfs

Let userspace know what the access map for the device is. This is helpful
for verifying that the access map is correctly configured and could also
be useful for programs that try to work with the data. File format is:

register: R W V P

where R, W, V and P are 'y' or 'n' showing readable, writable, volatile
and precious respectively.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regmap-debugfs.c

@@ -109,6 +109,73 @@ static const struct file_operations regmap_map_fops = {
 	.llseek = default_llseek,
 };
 
+static ssize_t regmap_access_read_file(struct file *file,
+				       char __user *user_buf, size_t count,
+				       loff_t *ppos)
+{
+	int reg_len, tot_len;
+	size_t buf_pos = 0;
+	loff_t p = 0;
+	ssize_t ret;
+	int i;
+	struct regmap *map = file->private_data;
+	char *buf;
+
+	if (*ppos < 0 || !count)
+		return -EINVAL;
+
+	buf = kmalloc(count, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	/* Calculate the length of a fixed format  */
+	reg_len = regmap_calc_reg_len(map->max_register, buf, count);
+	tot_len = reg_len + 10; /* ': R W V P\n' */
+
+	for (i = 0; i < map->max_register; i++) {
+		/* Ignore registers which are neither readable nor writable */
+		if (!regmap_readable(map, i) && !regmap_writeable(map, i))
+			continue;
+
+		/* If we're in the region the user is trying to read */
+		if (p >= *ppos) {
+			/* ...but not beyond it */
+			if (buf_pos >= count - 1 - tot_len)
+				break;
+
+			/* Format the register */
+			snprintf(buf + buf_pos, count - buf_pos,
+				 "%.*x: %c %c %c %c\n",
+				 reg_len, i,
+				 regmap_readable(map, i) ? 'y' : 'n',
+				 regmap_writeable(map, i) ? 'y' : 'n',
+				 regmap_volatile(map, i) ? 'y' : 'n',
+				 regmap_precious(map, i) ? 'y' : 'n');
+
+			buf_pos += tot_len;
+		}
+		p += tot_len;
+	}
+
+	ret = buf_pos;
+
+	if (copy_to_user(user_buf, buf, buf_pos)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	*ppos += buf_pos;
+
+out:
+	kfree(buf);
+	return ret;
+}
+
+static const struct file_operations regmap_access_fops = {
+	.open = regmap_open_file,
+	.read = regmap_access_read_file,
+	.llseek = default_llseek,
+};
 
 void regmap_debugfs_init(struct regmap *map)
 {
@@ -119,9 +186,12 @@ void regmap_debugfs_init(struct regmap *map)
 		return;
 	}
 
-	if (map->max_register)
+	if (map->max_register) {
 		debugfs_create_file("registers", 0400, map->debugfs,
 				    map, &regmap_map_fops);
+		debugfs_create_file("access", 0400, map->debugfs,
+				    map, &regmap_access_fops);
+	}
 }
 
 void regmap_debugfs_exit(struct regmap *map)