* [PATCH] media: i2c: Use div64_ul() for u64-by-unsigned-long divide
@ 2019-08-30 13:48 Geert Uytterhoeven
2019-08-31 9:38 ` Simon Horman
0 siblings, 1 reply; 2+ messages in thread
From: Geert Uytterhoeven @ 2019-08-30 13:48 UTC (permalink / raw)
To: Ramesh Shanmugasundaram, Mauro Carvalho Chehab
Cc: linux-media, linux-renesas-soc, 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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] media: i2c: Use div64_ul() for u64-by-unsigned-long divide
2019-08-30 13:48 [PATCH] media: i2c: Use div64_ul() for u64-by-unsigned-long divide Geert Uytterhoeven
@ 2019-08-31 9:38 ` Simon Horman
0 siblings, 0 replies; 2+ messages in thread
From: Simon Horman @ 2019-08-31 9:38 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: Ramesh Shanmugasundaram, Mauro Carvalho Chehab, linux-media,
linux-renesas-soc
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
>
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