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

Bjorn Andersson
2023-12-07T15:21:49Z

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
>