linux-kernel - [PATCH v2] clk: Avoid DT fetch in possible_parent_show if clk

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Message-ID: <20260205154202.21819-1-me@ziyao.cc>
Date: Thu,  5 Feb 2026 15:42:02 +0000
From: Yao Zi <me@...ao.cc>
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 <me@...ao.cc>,
	Drew Fustini <fustini@...nel.org>
Subject: [PATCH v2] 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 <me@...ao.cc>
Tested-by: Drew Fustini <fustini@...nel.org>
---
 drivers/clk/clk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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/

Changed from v1:
- Collect tags
- Switch to my new mail address
- Link to v1: https://lore.kernel.org/all/20250705095816.29480-2-ziyao@disroot.org/

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 85d2f2481acf..a9d1aea59689 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3588,7 +3588,7 @@ 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)";
-- 
2.52.0