clk: Add support for enabling/disabling clocks from debugfs

For test and debug purposes, it's simple enough to enable or disable
clocks from shell. Add a new debugfs file 'clk_prepare_enable' that
calls clk_prepare_enable() when writing "1" and clk_disable_unprepare()
when writing "0".

This can have security implications, so only support it when the code
has been modified to #define CLOCK_ALLOW_WRITE_DEBUGFS.
Signed-off-by: Mike Tipton <mdtipton@codeaurora.org>
Link: https://lore.kernel.org/r/20200630003024.6282-1-mdtipton@codeaurora.org
[sboyd@kernel.org: Reword commit text and remove comment update]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk.c

@@ -3039,6 +3039,31 @@ static int clk_rate_set(void *data, u64 val)
 }
 
 #define clk_rate_mode	0644
+
+static int clk_prepare_enable_set(void *data, u64 val)
+{
+	struct clk_core *core = data;
+	int ret = 0;
+
+	if (val)
+		ret = clk_prepare_enable(core->hw->clk);
+	else
+		clk_disable_unprepare(core->hw->clk);
+
+	return ret;
+}
+
+static int clk_prepare_enable_get(void *data, u64 *val)
+{
+	struct clk_core *core = data;
+
+	*val = core->enable_count && core->prepare_count;
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(clk_prepare_enable_fops, clk_prepare_enable_get,
+			 clk_prepare_enable_set, "%llu\n");
+
 #else
 #define clk_rate_set	NULL
 #define clk_rate_mode	0444
@@ -3216,6 +3241,10 @@ static void clk_debug_create_one(struct clk_core *core, struct dentry *pdentry)
 	debugfs_create_u32("clk_notifier_count", 0444, root, &core->notifier_count);
 	debugfs_create_file("clk_duty_cycle", 0444, root, core,
 			    &clk_duty_cycle_fops);
+#ifdef CLOCK_ALLOW_WRITE_DEBUGFS
+	debugfs_create_file("clk_prepare_enable", 0644, root, core,
+			    &clk_prepare_enable_fops);
+#endif
 
 	if (core->num_parents > 0)
 		debugfs_create_file("clk_parent", 0444, root, core,