linux-kernel - [PATCH] clk: Add support for enabling/disabling clocks from debugfs

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Message-Id: <20200630003024.6282-1-mdtipton@codeaurora.org>
Date:   Mon, 29 Jun 2020 17:30:24 -0700
From:   Mike Tipton <mdtipton@...eaurora.org>
To:     sboyd@...nel.org, mturquette@...libre.com
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        tdas@...eaurora.org, Mike Tipton <mdtipton@...eaurora.org>
Subject: [PATCH] clk: Add support for enabling/disabling clocks from debugfs

For test and debug purposes, it's often necessary 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_DEBUGS.

Signed-off-by: Mike Tipton <mdtipton@...eaurora.org>
---
 drivers/clk/clk.c | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 236923b25543..3640bbc56870 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3034,13 +3034,14 @@ static int clk_dump_show(struct seq_file *s, void *data)
 }
 DEFINE_SHOW_ATTRIBUTE(clk_dump);
 
-#undef CLOCK_ALLOW_WRITE_DEBUGFS
-#ifdef CLOCK_ALLOW_WRITE_DEBUGFS
 /*
- * This can be dangerous, therefore don't provide any real compile time
- * configuration option for this feature.
+ * These features can be dangerous, therefore don't provide any real compile
+ * time configuration option for them.
  * People who want to use this will need to modify the source code directly.
  */
+#undef CLOCK_ALLOW_WRITE_DEBUGFS
+#ifdef CLOCK_ALLOW_WRITE_DEBUGFS
+
 static int clk_rate_set(void *data, u64 val)
 {
 	struct clk_core *core = data;
@@ -3054,6 +3055,31 @@ 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
@@ -3231,6 +3257,10 @@ 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,
-- 
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