Re: [kvm-unit-tests PATCH v9 06/12] s390x: clock and delays caluculations

Cornelia Huck
2020-06-17T08:28:38Z

On Mon, 15 Jun 2020 11:31:55 +0200
Pierre Morel <pmorel@linux.ibm.com> wrote:

> The hardware gives us a good definition of the microsecond,
> let's keep this information and let the routine accessing
> the hardware keep all the information and return microseconds.
>
> Calculate delays in microseconds and take care about wrapping
> around zero.
>
> Define values with macros and use inlines to keep the
> milliseconds interface.
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
> lib/s390x/asm/time.h | 29 +++++++++++++++++++++++++++--
> 1 file changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/lib/s390x/asm/time.h b/lib/s390x/asm/time.h
> index 1791380..7f1d891 100644
> --- a/lib/s390x/asm/time.h
> +++ b/lib/s390x/asm/time.h
> @@ -13,14 +13,39 @@
> #ifndef ASM_S390X_TIME_H
> #define ASM_S390X_TIME_H
>
> -static inline uint64_t get_clock_ms(void)
> +#define STCK_SHIFT_US (63 - 51)
> +#define STCK_MAX ((1UL << 52) - 1)
> +
> +static inline uint64_t get_clock_us(void)
> {
> uint64_t clk;
>
> asm volatile(" stck %0 " : : "Q"(clk) : "memory");
>
> /* Bit 51 is incrememented each microsecond */

That comment may now be a tad non-obvious, because the details are
hidden behind the #define? Anyway, no strong opinion.

> - return (clk >> (63 - 51)) / 1000;
> + return clk >> STCK_SHIFT_US;
> +}
> +
> +static inline void udelay(unsigned long us)
> +{
> + unsigned long startclk = get_clock_us();
> + unsigned long c;
> +
> + do {
> + c = get_clock_us();
> + if (c < startclk)
> + c += STCK_MAX;
> + } while (c < startclk + us);
> +}
> +
> +static inline void mdelay(unsigned long ms)
> +{
> + udelay(ms * 1000);
> +}
> +
> +static inline uint64_t get_clock_ms(void)
> +{
> + return get_clock_us() / 1000;
> }
>
> #endif

Acked-by: Cornelia Huck <cohuck@redhat.com>