clk: add clk_possible_parents debugfs file

For validation purposes, it's often useful to be able to retrieve the list
of possible parents in userspace. Add a debugfs file for every clock which
has more than 1 possible parent.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Reviewed-by: Jon Mayo <jmayo@nvidia.com>
[sboyd@codeaurora.org: Remove useless cast from void and extra
newline]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>

drivers/clk/clk.c

@@ -2126,6 +2126,31 @@ static const struct file_operations clk_dump_fops = {
 	.release	= single_release,
 };
 
+static int possible_parents_dump(struct seq_file *s, void *data)
+{
+	struct clk_core *core = s->private;
+	int i;
+
+	for (i = 0; i < core->num_parents - 1; i++)
+		seq_printf(s, "%s ", core->parent_names[i]);
+
+	seq_printf(s, "%s\n", core->parent_names[i]);
+
+	return 0;
+}
+
+static int possible_parents_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, possible_parents_dump, inode->i_private);
+}
+
+static const struct file_operations possible_parents_fops = {
+	.open		= possible_parents_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 static int clk_debug_create_one(struct clk_core *core, struct dentry *pdentry)
 {
 	struct dentry *d;
@@ -2177,6 +2202,13 @@ static int clk_debug_create_one(struct clk_core *core, struct dentry *pdentry)
 	if (!d)
 		goto err_out;
 
+	if (core->num_parents > 1) {
+		d = debugfs_create_file("clk_possible_parents", S_IRUGO,
+				core->dentry, core, &possible_parents_fops);
+		if (!d)
+			goto err_out;
+	}
+
 	if (core->ops->debug_init) {
 		ret = core->ops->debug_init(core->hw, core->dentry);
 		if (ret)