diff mbox series

[1/2] soc: qcom: stats: fix 64-bit division

Message ID 20231206123717.524009-1-arnd@kernel.org
State New
Headers
Series [1/2] soc: qcom: stats: fix 64-bit division |

Commit Message

Arnd Bergmann Dec. 6, 2023, 12:37 p.m. UTC 
  From: Arnd Bergmann <arnd@arndb.de>

Unguarded 64-bit division is not allowed on 32-bit kernels because this
is very slow. The result of trying anyway is a link failure:

arm-linux-gnueabi-ld: drivers/soc/qcom/qcom_stats.o: in function `qcom_ddr_stats_show':
qcom_stats.c:(.text+0x334): undefined reference to `__aeabi_uldivmod'

As this function is only used for debugging and not performance critical,
rewrite it to use div_u64() instead. ARCH_TIMER_FREQ is a multiple of
MSEC_PER_SEC anyway, so there is no loss in precisison.

Fixes: e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/soc/qcom/qcom_stats.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Uwe Kleine-König Dec. 6, 2023, 2:16 p.m. UTC | #1 
Hallo Arnd,

On Wed, Dec 06, 2023 at 01:37:06PM +0100, Arnd Bergmann wrote:
> Unguarded 64-bit division is not allowed on 32-bit kernels because this
> is very slow. The result of trying anyway is a link failure:
> 
> arm-linux-gnueabi-ld: drivers/soc/qcom/qcom_stats.o: in function `qcom_ddr_stats_show':
> qcom_stats.c:(.text+0x334): undefined reference to `__aeabi_uldivmod'
> 
> As this function is only used for debugging and not performance critical,
> rewrite it to use div_u64() instead. ARCH_TIMER_FREQ is a multiple of
> MSEC_PER_SEC anyway, so there is no loss in precisison.

Maybe add this information in a comment?

We have

	#define ARCH_TIMER_FREQ         19200000

so it's a multiple of MSEC_PER_SEC (= 1000) indeed.

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Best regards
Uwe
Bjorn Andersson Dec. 7, 2023, 3:24 p.m. UTC | #2 
On Wed, Dec 06, 2023 at 01:37:06PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Unguarded 64-bit division is not allowed on 32-bit kernels because this
> is very slow. The result of trying anyway is a link failure:
> 
> arm-linux-gnueabi-ld: drivers/soc/qcom/qcom_stats.o: in function `qcom_ddr_stats_show':
> qcom_stats.c:(.text+0x334): undefined reference to `__aeabi_uldivmod'
> 
> As this function is only used for debugging and not performance critical,
> rewrite it to use div_u64() instead. ARCH_TIMER_FREQ is a multiple of
> MSEC_PER_SEC anyway, so there is no loss in precisison.
> 
> Fixes: e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

I had [1] lined up already, but hadn't pushed the branch out out... Like
your version better, so dropping mine.

[1] https://lore.kernel.org/all/20231205-qcom_stats-aeabi_uldivmod-fix-v1-1-f94ecec5e894@quicinc.com/

Thanks,
Bjorn

> ---
>  drivers/soc/qcom/qcom_stats.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/qcom/qcom_stats.c b/drivers/soc/qcom/qcom_stats.c
> index 4763d62a8cb0..5ec8a754b22b 100644
> --- a/drivers/soc/qcom/qcom_stats.c
> +++ b/drivers/soc/qcom/qcom_stats.c
> @@ -221,7 +221,7 @@ static int qcom_ddr_stats_show(struct seq_file *s, void *unused)
>  
>  	for (i = 0; i < ddr.entry_count; i++) {
>  		/* Convert the period to ms */
> -		entry[i].dur = mult_frac(MSEC_PER_SEC, entry[i].dur, ARCH_TIMER_FREQ);
> +		entry[i].dur = div_u64(entry[i].dur, ARCH_TIMER_FREQ / MSEC_PER_SEC);
>  	}
>  
>  	for (i = 0; i < ddr.entry_count; i++)
> -- 
> 2.39.2
>
Bjorn Andersson Dec. 8, 2023, 2:55 p.m. UTC | #3 
On Wed, 06 Dec 2023 13:37:06 +0100, Arnd Bergmann wrote:
> Unguarded 64-bit division is not allowed on 32-bit kernels because this
> is very slow. The result of trying anyway is a link failure:
> 
> arm-linux-gnueabi-ld: drivers/soc/qcom/qcom_stats.o: in function `qcom_ddr_stats_show':
> qcom_stats.c:(.text+0x334): undefined reference to `__aeabi_uldivmod'
> 
> As this function is only used for debugging and not performance critical,
> rewrite it to use div_u64() instead. ARCH_TIMER_FREQ is a multiple of
> MSEC_PER_SEC anyway, so there is no loss in precisison.
> 
> [...]

Applied, thanks!

[1/2] soc: qcom: stats: fix 64-bit division
      commit: 73380e2573c34a45e01786750a4a2efafc2248bd

Best regards,
diff mbox series

Patch

diff --git a/drivers/soc/qcom/qcom_stats.c b/drivers/soc/qcom/qcom_stats.c
index 4763d62a8cb0..5ec8a754b22b 100644
--- a/drivers/soc/qcom/qcom_stats.c
+++ b/drivers/soc/qcom/qcom_stats.c
@@ -221,7 +221,7 @@  static int qcom_ddr_stats_show(struct seq_file *s, void *unused)
 
 	for (i = 0; i < ddr.entry_count; i++) {
 		/* Convert the period to ms */
-		entry[i].dur = mult_frac(MSEC_PER_SEC, entry[i].dur, ARCH_TIMER_FREQ);
+		entry[i].dur = div_u64(entry[i].dur, ARCH_TIMER_FREQ / MSEC_PER_SEC);
 	}
 
 	for (i = 0; i < ddr.entry_count; i++)