[PATCH] time: Use div64_long() instead of do_div()

[PATCH] time: Use div64_long() instead of do_div()

[Thorsten Blum]

Fixes Coccinelle/coccicheck warning reported by do_div.cocci.

Compared to do_div(), div64_long() does not implicitly cast the divisor and
does not unnecessarily calculate the remainder.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
---
 kernel/time/jiffies.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index bc4db9e5ab70..9d23178e2b6a 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -91,7 +91,7 @@ int register_refined_jiffies(long cycles_per_second)
 	/* shift_hz stores hz<<8 for extra accuracy */
 	shift_hz = (u64)cycles_per_second << 8;
 	shift_hz += cycles_per_tick/2;
-	do_div(shift_hz, cycles_per_tick);
+	shift_hz = div64_long(shift_hz, cycles_per_tick);
 	/* Calculate nsec_per_tick using shift_hz */
 	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
 	nsec_per_tick += (u32)shift_hz/2;
-- 
2.43.2

Re: [PATCH] time: Use div64_long() instead of do_div()

[Liao, Chang]

Thorsten,

在 2024/2/26 7:25, Thorsten Blum 写道:
> Fixes Coccinelle/coccicheck warning reported by do_div.cocci.
> 
> Compared to do_div(), div64_long() does not implicitly cast the divisor and
> does not unnecessarily calculate the remainder.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
> ---
>  kernel/time/jiffies.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
> index bc4db9e5ab70..9d23178e2b6a 100644
> --- a/kernel/time/jiffies.c
> +++ b/kernel/time/jiffies.c
> @@ -91,7 +91,7 @@ int register_refined_jiffies(long cycles_per_second)
>  	/* shift_hz stores hz<<8 for extra accuracy */
>  	shift_hz = (u64)cycles_per_second << 8;
>  	shift_hz += cycles_per_tick/2;
> -	do_div(shift_hz, cycles_per_tick);
> +	shift_hz = div64_long(shift_hz, cycles_per_tick);

I am considering using div64_ul() to calculate the result. as shift_hz is
unsigned long, assume the sign bit of divisor cycles_per_tick never be set
in this context,then div64_long() will do a extra sign extension for result.
Or are there other recommendations?

Thanks.

>  	/* Calculate nsec_per_tick using shift_hz */
>  	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
>  	nsec_per_tick += (u32)shift_hz/2;

-- 
BR
Liao, Chang

Re: [PATCH] time: Use div64_long() instead of do_div()

[Thorsten Blum]

> On Feb 26, 2024, at 04:28, Liao, Chang <liaochang1@huawei.com> wrote:
> 
> I am considering using div64_ul() to calculate the result. as shift_hz is
> unsigned long, assume the sign bit of divisor cycles_per_tick never be set
> in this context,then div64_long() will do a extra sign extension for result.

Yes, div64_ul() is better and also removes the warning.

I'll submit a v2 shortly.

Thanks,
Thorsten

[PATCH v2] time: Use div64_ul() instead of do_div()

[Thorsten Blum]

Fixes Coccinelle/coccicheck warning reported by do_div.cocci.

Compared to do_div(), div64_ul() does not implicitly cast the divisor and
does not unnecessarily calculate the remainder.

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
---
Changes in v2:
- s/div64_long/div64_ul/ as suggested by Chang Liao
---
 kernel/time/jiffies.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index bc4db9e5ab70..fccee15e94d5 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -91,7 +91,7 @@ int register_refined_jiffies(long cycles_per_second)
 	/* shift_hz stores hz<<8 for extra accuracy */
 	shift_hz = (u64)cycles_per_second << 8;
 	shift_hz += cycles_per_tick/2;
-	do_div(shift_hz, cycles_per_tick);
+	shift_hz = div64_ul(shift_hz, cycles_per_tick);
 	/* Calculate nsec_per_tick using shift_hz */
 	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
 	nsec_per_tick += (u32)shift_hz/2;
-- 
2.43.2

Re: [PATCH v2] time: Use div64_ul() instead of do_div()

[Liao, Chang]

在 2024/2/26 17:03, Thorsten Blum 写道:
> Fixes Coccinelle/coccicheck warning reported by do_div.cocci.
> 
> Compared to do_div(), div64_ul() does not implicitly cast the divisor and
> does not unnecessarily calculate the remainder.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
> ---
> Changes in v2:
> - s/div64_long/div64_ul/ as suggested by Chang Liao
> ---
>  kernel/time/jiffies.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
> index bc4db9e5ab70..fccee15e94d5 100644
> --- a/kernel/time/jiffies.c
> +++ b/kernel/time/jiffies.c
> @@ -91,7 +91,7 @@ int register_refined_jiffies(long cycles_per_second)
>  	/* shift_hz stores hz<<8 for extra accuracy */
>  	shift_hz = (u64)cycles_per_second << 8;
>  	shift_hz += cycles_per_tick/2;
> -	do_div(shift_hz, cycles_per_tick);
> +	shift_hz = div64_ul(shift_hz, cycles_per_tick);

LGTM

Reviewed-by: Liao Chang <liaochang1@huawei.com>

>  	/* Calculate nsec_per_tick using shift_hz */
>  	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
>  	nsec_per_tick += (u32)shift_hz/2;

-- 
BR
Liao, Chang