[PATCH] media: i2c: Use div64_ul() for u64-by-unsigned-long divide

[PATCH] media: i2c: Use div64_ul() for u64-by-unsigned-long divide

[Geert Uytterhoeven]

div_u64() does a 64-by-32 division, while the divisor max2175.xtal_freq
is unsigned long, thus 64-bit on 64-bit platforms.  Hence the proper
function to call is div64_ul().

Note that this change does not have any functional impact, as the
crystal frequency must be much lower than the 32-bit limit anyway.
On 32-bit platforms, the generated code is the same.  But at least on
arm64, this saves an AND-instruction to truncate xtal_freq to 32-bit.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/media/i2c/max2175.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/i2c/max2175.c b/drivers/media/i2c/max2175.c
index 19a3ceea3bc20f0f..506a30e69ced45c4 100644
--- a/drivers/media/i2c/max2175.c
+++ b/drivers/media/i2c/max2175.c
@@ -591,8 +591,8 @@ static int max2175_set_lo_freq(struct max2175 *ctx, u32 lo_freq)
 		lo_freq *= lo_mult;
 
 	int_desired = lo_freq / ctx->xtal_freq;
-	frac_desired = div_u64((u64)(lo_freq % ctx->xtal_freq) << 20,
-			       ctx->xtal_freq);
+	frac_desired = div64_ul((u64)(lo_freq % ctx->xtal_freq) << 20,
+				ctx->xtal_freq);
 
 	/* Check CSM is not busy */
 	ret = max2175_poll_csm_ready(ctx);
-- 
2.17.1

Re: [PATCH] media: i2c: Use div64_ul() for u64-by-unsigned-long divide

[Simon Horman]

On Fri, Aug 30, 2019 at 03:48:27PM +0200, Geert Uytterhoeven wrote:
> div_u64() does a 64-by-32 division, while the divisor max2175.xtal_freq
> is unsigned long, thus 64-bit on 64-bit platforms.  Hence the proper
> function to call is div64_ul().
> 
> Note that this change does not have any functional impact, as the
> crystal frequency must be much lower than the 32-bit limit anyway.
> On 32-bit platforms, the generated code is the same.  But at least on
> arm64, this saves an AND-instruction to truncate xtal_freq to 32-bit.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Reviewed-by: Simon Horman <horms+renesas@verge.net.au>

> ---
>  drivers/media/i2c/max2175.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/i2c/max2175.c b/drivers/media/i2c/max2175.c
> index 19a3ceea3bc20f0f..506a30e69ced45c4 100644
> --- a/drivers/media/i2c/max2175.c
> +++ b/drivers/media/i2c/max2175.c
> @@ -591,8 +591,8 @@ static int max2175_set_lo_freq(struct max2175 *ctx, u32 lo_freq)
>  		lo_freq *= lo_mult;
>  
>  	int_desired = lo_freq / ctx->xtal_freq;
> -	frac_desired = div_u64((u64)(lo_freq % ctx->xtal_freq) << 20,
> -			       ctx->xtal_freq);
> +	frac_desired = div64_ul((u64)(lo_freq % ctx->xtal_freq) << 20,
> +				ctx->xtal_freq);
>  
>  	/* Check CSM is not busy */
>  	ret = max2175_poll_csm_ready(ctx);
> -- 
> 2.17.1
>