linux-kernel - [PATCH] clk: Avoid DT fetch in possible_parent_show if clk

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Message-ID: <20250705095816.29480-2-ziyao@disroot.org>
Date: Sat,  5 Jul 2025 09:58:17 +0000
From: Yao Zi <ziyao@...root.org>
To: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Chen-Yu Tsai <wens@...e.org>
Cc: linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yao Zi <ziyao@...root.org>
Subject: [PATCH] clk: Avoid DT fetch in possible_parent_show if clk_hw is provided

When showing a parent for which clk_core_get_parent_by_index fails, we
may try using the parent's global name or the local name. If this fails
either, the parent clock's clock-output-names is fetched through
DT-index.

struct clk_hw pointer takes precedence with DT-index when registering
clocks, thus most drivers only zero the index member of struct
clk_parent_data when providing the parent through struct clk_hw pointer.
If the pointer cannot resovle to a clock, clk_core_get_parent_by_index
will fail as well, in which case possible_parent_show will fetch the
parent's clock-output-names property, treat the unintended, zeroed index
as valid, and yield a misleading name if the clock controller does come
with a clocks property.

Let's add an extra check against the struct clk_hw pointer, and only
perform the DT-index-based fetch if it isn't provided.

Fixes: 2d156b78ce8f ("clk: Fix debugfs clk_possible_parents for clks without parent string names")
Signed-off-by: Yao Zi <ziyao@...root.org>
---

This was found when fixing the wrong parent description of
clk-th1520-ap.c[1]. Without the patch,

	# cat /sys/kernel/debug/clk/c910/clk_possible_parents
	osc_24m cpu-pll1

The first parent should be c910-i0, provided by an unresolvable struct
clk_hw pointer. osc_24m is the first (and only) parent specified in
devicetree for the clock controller. With the patch,

	# cat /sys/kernel/debug/clk/c910/clk_possible_parents
	(missing) cpu-pll1

[1]: https://lore.kernel.org/linux-riscv/20250705052028.24611-1-ziyao@disroot.org/

 drivers/clk/clk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 0565c87656cf..280d3a470228 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3594,7 +3594,7 @@ static void possible_parent_show(struct seq_file *s, struct clk_core *core,
 	} else if (core->parents[i].fw_name) {
 		seq_printf(s, "<%s>(fw)", core->parents[i].fw_name);
 	} else {
-		if (core->parents[i].index >= 0)
+		if (!core->parents[i].hw && core->parents[i].index >= 0)
 			name = of_clk_get_parent_name(core->of_node, core->parents[i].index);
 		if (!name)
 			name = "(missing)";
-- 
2.49.0