[PATCH] clk: use ULONG_MAX as the initial value for the iteration in clk_mux_determine_rate_flags()

[PATCH] clk: use ULONG_MAX as the initial value for the iteration in clk_mux_determine_rate_flags()

[Yang Xiwen via B4 Relay]

From: Yang Xiwen <forbidden405@outlook.com>

Currently, clk_mux_determine_rate_flags() use 0 as the initial value for
selecting the best matching parent. However, this will choose a
non-existant rate(0) if the requested rate is closer to 0 than the
minimum rate the parents have.

Fix that by initializing the initial value to ULONG_MAX and treat it as a
magic number.

Signed-off-by: Yang Xiwen <forbidden405@outlook.com>
---
 drivers/clk/clk.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index ae07685c7588b..ab8a2acfac8f3 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -541,6 +541,9 @@ EXPORT_SYMBOL_GPL(__clk_is_enabled);
 static bool mux_is_better_rate(unsigned long rate, unsigned long now,
 			   unsigned long best, unsigned long flags)
 {
+	if (best == ULONG_MAX)
+		return true;
+
 	if (flags & CLK_MUX_ROUND_CLOSEST)
 		return abs(now - rate) < abs(best - rate);
 
@@ -600,7 +603,7 @@ int clk_mux_determine_rate_flags(struct clk_hw *hw,
 {
 	struct clk_core *core = hw->core, *parent, *best_parent = NULL;
 	int i, num_parents, ret;
-	unsigned long best = 0;
+	unsigned long best = ULONG_MAX;
 
 	/* if NO_REPARENT flag set, pass through to current parent */
 	if (core->flags & CLK_SET_RATE_NO_REPARENT) {

---
base-commit: 76f598ba7d8e2bfb4855b5298caedd5af0c374a8
change-id: 20230421-clk-64c6b6e21cdb

Best regards,
-- 
Yang Xiwen <forbidden405@outlook.com>

Re: [PATCH] clk: use ULONG_MAX as the initial value for the iteration in clk_mux_determine_rate_flags()

[Stephen Boyd]

Quoting Yang Xiwen via B4 Relay (2023-04-21 08:56:38)
> From: Yang Xiwen <forbidden405@outlook.com>
> 
> Currently, clk_mux_determine_rate_flags() use 0 as the initial value for
> selecting the best matching parent. However, this will choose a
> non-existant rate(0) if the requested rate is closer to 0 than the
> minimum rate the parents have.
> 
> Fix that by initializing the initial value to ULONG_MAX and treat it as a
> magic number.

Can you add a unit test to clk_test.c as well?