linux-kernel - [PATCH v2 2/2] clk: divider: Fix divisions

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Message-Id: <20230526171057.66876-3-sebastian.reichel@collabora.com>
Date:   Fri, 26 May 2023 19:10:57 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Christopher Obbard <chris.obbard@...labora.com>,
        David Laight <David.Laight@...LAB.COM>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        kernel@...labora.com
Subject: [PATCH v2 2/2] clk: divider: Fix divisions

The clock framework handles clock rates as "unsigned long", so u32 on
32-bit architectures and u64 on 64-bit architectures.

The current code pointlessly casts the dividend to u64 on 32-bit
architectures and thus pointlessly reducing the performance.

On the other hand on 64-bit architectures the divisor is masked and only
the lower 32-bit are used. Thus requesting a frequency >= 4.3GHz results
in incorrect values. For example requesting 4300000000 (4.3 GHz) will
effectively request ca. 5 MHz. Requesting clk_round_rate(clk, ULONG_MAX)
is a bit of a special case, since that still returns correct values as
long as the parent clock is below 8.5 GHz.

Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
---
 drivers/clk/clk-divider.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index a2c2b5203b0a..c38e8aa60e54 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -220,7 +220,7 @@ static int _div_round_up(const struct clk_div_table *table,
 			 unsigned long parent_rate, unsigned long rate,
 			 unsigned long flags)
 {
-	int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
+	int div = DIV_ROUND_UP(parent_rate, rate);
 
 	if (flags & CLK_DIVIDER_POWER_OF_TWO)
 		div = __roundup_pow_of_two(div);
@@ -237,7 +237,7 @@ static int _div_round_closest(const struct clk_div_table *table,
 	int up, down;
 	unsigned long up_rate, down_rate;
 
-	up = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
+	up = DIV_ROUND_UP(parent_rate, rate);
 	down = parent_rate / rate;
 
 	if (flags & CLK_DIVIDER_POWER_OF_TWO) {
@@ -473,7 +473,7 @@ int divider_get_val(unsigned long rate, unsigned long parent_rate,
 {
 	unsigned int div, value;
 
-	div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
+	div = DIV_ROUND_UP(parent_rate, rate);
 
 	if (!_is_valid_div(table, div, flags))
 		return -EINVAL;
-- 
2.39.2