linux-kernel - [PATCH] clk: Allow phase adjustment from debugfs

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Message-Id: <20230420103805.125246-1-john@metanate.com>
Date:   Thu, 20 Apr 2023 11:38:04 +0100
From:   John Keeping <john@...anate.com>
To:     linux-clk@...r.kernel.org
Cc:     John Keeping <john@...anate.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] clk: Allow phase adjustment from debugfs

For testing it may be useful to manually adjust a clock's phase.  Add
support for writing to the existing clk_phase debugfs file, with the
written value clamped to [0, 360) to match the behaviour of the
clk_set_phase() function.

This is a dangerous feature, so use the existing define
CLOCK_ALLOW_WRITE_DEBUGFS to allow it only if the source is modified.

Signed-off-by: John Keeping <john@...anate.com>
---
 drivers/clk/clk.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 27c30a533759..2d3b6869f3f6 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3297,6 +3297,21 @@ static int clk_rate_set(void *data, u64 val)
 
 #define clk_rate_mode	0644
 
+static int clk_phase_set(void *data, u64 val)
+{
+	struct clk_core *core = data;
+	int degrees = do_div(val, 360);
+	int ret;
+
+	clk_prepare_lock();
+	ret = clk_core_set_phase_nolock(core, degrees);
+	clk_prepare_unlock();
+
+	return ret;
+}
+
+#define clk_phase_mode	0644
+
 static int clk_prepare_enable_set(void *data, u64 val)
 {
 	struct clk_core *core = data;
@@ -3324,6 +3339,9 @@ DEFINE_DEBUGFS_ATTRIBUTE(clk_prepare_enable_fops, clk_prepare_enable_get,
 #else
 #define clk_rate_set	NULL
 #define clk_rate_mode	0444
+
+#define clk_phase_set	NULL
+#define clk_phase_mode	0644
 #endif
 
 static int clk_rate_get(void *data, u64 *val)
@@ -3339,6 +3357,16 @@ static int clk_rate_get(void *data, u64 *val)
 
 DEFINE_DEBUGFS_ATTRIBUTE(clk_rate_fops, clk_rate_get, clk_rate_set, "%llu\n");
 
+static int clk_phase_get(void *data, u64 *val)
+{
+	struct clk_core *core = data;
+
+	*val = core->phase;
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(clk_phase_fops, clk_phase_get, clk_phase_set, "%llu\n");
+
 static const struct {
 	unsigned long flag;
 	const char *name;
@@ -3529,7 +3557,8 @@ static void clk_debug_create_one(struct clk_core *core, struct dentry *pdentry)
 	debugfs_create_file("clk_min_rate", 0444, root, core, &clk_min_rate_fops);
 	debugfs_create_file("clk_max_rate", 0444, root, core, &clk_max_rate_fops);
 	debugfs_create_ulong("clk_accuracy", 0444, root, &core->accuracy);
-	debugfs_create_u32("clk_phase", 0444, root, &core->phase);
+	debugfs_create_file("clk_phase", clk_phase_mode, root, core,
+			    &clk_phase_fops);
 	debugfs_create_file("clk_flags", 0444, root, core, &clk_flags_fops);
 	debugfs_create_u32("clk_prepare_count", 0444, root, &core->prepare_count);
 	debugfs_create_u32("clk_enable_count", 0444, root, &core->enable_count);
-- 
2.40.0