linux-kernel - [PATCH] clk: Add fault tolerance to of_clk_hw_onecell

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Message-Id: <20250731-add_fault_tolerance_to_of_clk_hw_onecell_get-v1-1-886214fab4a7@amlogic.com>
Date: Thu, 31 Jul 2025 20:39:58 +0800
From: Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org>
To: Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>
Cc: linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Chuan Liu <chuan.liu@...ogic.com>
Subject: [PATCH] clk: Add fault tolerance to of_clk_hw_onecell_get()

From: Chuan Liu <chuan.liu@...ogic.com>

In specific cases, even a clk_provider managing only a single clock may
reference of_clk_hw_onecell_get() to access its member clocks, as seen
in implementations like clk-scmi.

For a clk_provider with only one clock, when calling
of_parse_phandle_with_args(), the phandle_args->args[] members are not
assigned. In this case, the reference to phandle_args->args[0] in
of_clk_hw_onecell_get() becomes invalid. If phandle_args->args[0]
initially contains a non-zero value, this will trigger an error.

Signed-off-by: Chuan Liu <chuan.liu@...ogic.com>
---
Error conditions observed:

scmi_clk: protocol@14 {
	reg = <0x14>;
	#clock-cells = <0>;
};

phandle1: clock-controller@1 {
	#clock-cells = <1>;
}

clock-consumer@2 {
	assigned-clocks = <&phandle1 1>,
			  <&scmi_clk>;
	assigned-clock-rates = <xxx>,
			       <xxx>;
}

Under these conditions, executing of_clk_set_defaults() triggers the
error: 'of_clk_hw_onecell_get: invalid index 1'.

While the root cause lies in invalid input data to
of_clk_hw_onecell_get(), checking phandle->args_count for data validity
improves driver fault tolerance.
---
 drivers/clk/clk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 0565c87656cf..4994c551befe 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -4966,7 +4966,7 @@ EXPORT_SYMBOL_GPL(of_clk_hw_simple_get);
 struct clk *of_clk_src_onecell_get(struct of_phandle_args *clkspec, void *data)
 {
 	struct clk_onecell_data *clk_data = data;
-	unsigned int idx = clkspec->args[0];
+	unsigned int idx = clkspec->args_count ? clkspec->args[0] : 0;
 
 	if (idx >= clk_data->clk_num) {
 		pr_err("%s: invalid clock index %u\n", __func__, idx);
@@ -4981,7 +4981,7 @@ struct clk_hw *
 of_clk_hw_onecell_get(struct of_phandle_args *clkspec, void *data)
 {
 	struct clk_hw_onecell_data *hw_data = data;
-	unsigned int idx = clkspec->args[0];
+	unsigned int idx = clkspec->args_count ? clkspec->args[0] : 0;
 
 	if (idx >= hw_data->num) {
 		pr_err("%s: invalid index %u\n", __func__, idx);

---
base-commit: 58abdca0eb653c1a2e755ba9ba406ee475d87636
change-id: 20250730-add_fault_tolerance_to_of_clk_hw_onecell_get-fdc81f7e35a5

Best regards,
-- 
Chuan Liu <chuan.liu@...ogic.com>