[PATCH] i2c: mlxbf: avoid 64-bit division

[PATCH] i2c: mlxbf: avoid 64-bit division

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

The 64-bit division in mlxbf_i2c_get_ticks() causes link failures
when compile-testing on 32-bit machines:

ERROR: modpost: "__udivdi3" [drivers/i2c/busses/i2c-mlxbf.ko] undefined!

Change this to a div_u64(), which should replace the constant division
with a a multiply/shift combination in the mlxbf_i2c_get_ticks().

The frequency calculation functions require a slow library call but
should be used much rarer.

Fixes: 9c6c6fa671f9 ("i2c: mlxbf: Allow build with COMPILE_TEST")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/i2c/busses/i2c-mlxbf.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mlxbf.c b/drivers/i2c/busses/i2c-mlxbf.c
index 39359942e4d7..8345f7e6385d 100644
--- a/drivers/i2c/busses/i2c-mlxbf.c
+++ b/drivers/i2c/busses/i2c-mlxbf.c
@@ -1083,7 +1083,7 @@ static u32 mlxbf_i2c_get_ticks(struct mlxbf_i2c_priv *priv, u64 nanoseconds,
 	 *         Frequency
 	 */
 	frequency = priv->frequency;
-	ticks = (nanoseconds * frequency) / MLXBF_I2C_FREQUENCY_1GHZ;
+	ticks = div_u64(nanoseconds * frequency, MLXBF_I2C_FREQUENCY_1GHZ);
 	/*
 	 * The number of ticks is rounded down and if minimum is equal to 1
 	 * then add one tick.
@@ -1460,9 +1460,8 @@ static u64 mlxbf_i2c_calculate_freq_from_tyu(struct mlxbf_i2c_resource *corepll_
 	 * and PadFrequency, respectively.
 	 */
 	core_frequency = MLXBF_I2C_PLL_IN_FREQ * (++core_f);
-	core_frequency /= (++core_r) * (++core_od);
 
-	return core_frequency;
+	return div_u64(core_frequency, (++core_r) * (++core_od));
 }
 
 static u64 mlxbf_i2c_calculate_freq_from_yu(struct mlxbf_i2c_resource *corepll_res)
@@ -1491,9 +1490,8 @@ static u64 mlxbf_i2c_calculate_freq_from_yu(struct mlxbf_i2c_resource *corepll_r
 	 * and PadFrequency, respectively.
 	 */
 	corepll_frequency = (MLXBF_I2C_PLL_IN_FREQ * core_f) / MLNXBF_I2C_COREPLL_CONST;
-	corepll_frequency /= (++core_r) * (++core_od);
 
-	return corepll_frequency;
+	return div_u64(corepll_frequency, (++core_r) * (++core_od));
 }
 
 static int mlxbf_i2c_calculate_corepll_freq(struct platform_device *pdev,
-- 
2.39.5

Re: [PATCH] i2c: mlxbf: avoid 64-bit division

[Andi Shyti]

Hi Arnd,

On Tue, May 20, 2025 at 05:25:45PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The 64-bit division in mlxbf_i2c_get_ticks() causes link failures
> when compile-testing on 32-bit machines:
> 
> ERROR: modpost: "__udivdi3" [drivers/i2c/busses/i2c-mlxbf.ko] undefined!
> 
> Change this to a div_u64(), which should replace the constant division
> with a a multiply/shift combination in the mlxbf_i2c_get_ticks().
> 
> The frequency calculation functions require a slow library call but
> should be used much rarer.
> 
> Fixes: 9c6c6fa671f9 ("i2c: mlxbf: Allow build with COMPILE_TEST")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

merged to i2c/i2c-host.

Thanks,
Andi