linux-kernel - [PATCH v2 1/2] clk: set initial best mux parent to current parent when determining rate

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Date: Wed, 06 Mar 2024 00:22:23 +0800
From: Yang Xiwen via B4 Relay <devnull+forbidden405.outlook.com@...nel.org>
To: Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>
Cc: Maxime Ripard <mripard@...nel.org>, linux-clk@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Yang Xiwen <forbidden405@...look.com>
Subject: [PATCH v2 1/2] clk: set initial best mux parent to current parent
 when determining rate

From: Yang Xiwen <forbidden405@...look.com>

Originally, the initial clock rate is hardcoded to 0, this can lead to
some problem when setting a very small rate with CLK_MUX_ROUND_CLOSEST.

For example, if the lowest possible rate provided by the mux is 1000Hz,
setting a rate below 500Hz will fail, because no clock can provide a
better rate than the non-existant 0Hz. But it should succeed with 1000Hz
being set.

Setting the initial best parent to current parent could solve this bug.

Signed-off-by: Yang Xiwen <forbidden405@...look.com>
---
 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 2253c154a824..5fa92227b355 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -639,9 +639,9 @@ int clk_mux_determine_rate_flags(struct clk_hw *hw,
 				 struct clk_rate_request *req,
 				 unsigned long flags)
 {
-	struct clk_core *core = hw->core, *parent, *best_parent = NULL;
+	struct clk_core *core = hw->core, *parent, *best_parent = core->parent;
 	int i, num_parents, ret;
-	unsigned long best = 0;
+	unsigned long best = clk_core_get_rate_nolock(core);
 
 	/* if NO_REPARENT flag set, pass through to current parent */
 	if (core->flags & CLK_SET_RATE_NO_REPARENT)

-- 
2.43.0