regmap: Add support for writing to regmap registers via debugfs

To enable writing to the regmap debugfs registers file users will
need to modify the source directly and #define REGMAP_ALLOW_WRITE_DEBUGFS.
The reason for this is that it is dangerous to expose this
functionality in general where clients could potentially be PMICs.

[A couple of minor style updates -- broonie]

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
index b3b4b8f7f409..7accb81dd94e 100644
--- a/drivers/base/regmap/regmap-debugfs.c
+++ b/drivers/base/regmap/regmap-debugfs.c
@@ -103,9 +103,51 @@ out:
         return ret;
 }
 
+#undef REGMAP_ALLOW_WRITE_DEBUGFS
+#ifdef REGMAP_ALLOW_WRITE_DEBUGFS
+/*
+ * This can be dangerous especially when we have clients such as
+ * PMICs, therefore don't provide any real compile time configuration option
+ * for this feature, people who want to use this will need to modify
+ * the source code directly.
+ */
+static ssize_t regmap_map_write_file(struct file *file,
+                                     const char __user *user_buf,
+                                     size_t count, loff_t *ppos)
+{
+        char buf[32];
+        size_t buf_size;
+        char *start = buf;
+        unsigned long reg, value;
+        struct regmap *map = file->private_data;
+
+        buf_size = min(count, (sizeof(buf)-1));
+        if (copy_from_user(buf, user_buf, buf_size))
+                return -EFAULT;
+        buf[buf_size] = 0;
+
+        while (*start == ' ')
+                start++;
+        reg = simple_strtoul(start, &start, 16);
+        while (*start == ' ')
+                start++;
+        if (strict_strtoul(start, 16, &value))
+                return -EINVAL;
+
+        /* Userspace has been fiddling around behind the kernel's back */
+        add_taint(TAINT_USER);
+
+        regmap_write(map, reg, value);
+        return buf_size;
+}
+#else
+#define regmap_map_write_file NULL
+#endif
+
 static const struct file_operations regmap_map_fops = {
         .open = regmap_open_file,
         .read = regmap_map_read_file,
+        .write = regmap_map_write_file,
         .llseek = default_llseek,
 };