On 30.04.24 10:52, [email protected] wrote:
> From: Lakshmi Sowjanya D <[email protected]>
>
> Add base clock hardware abstraction in clocksource structure.
>
> Provide generic functionality in convert_base_to_cs() to convert base
> clock timestamps to system clocksource without requiring architecture
> specific parameters.
>
> This is intended to replace convert_art_to_tsc() and
> convert_art_ns_to_tsc() functions which are specific to convert ART
> (Always Running Timer) time to the corresponding TSC value.
>
> Add the infrastructure in get_device_system_crosststamp().
>
> Co-developed-by: Thomas Gleixner <[email protected]>
> Signed-off-by: Thomas Gleixner <[email protected]>
> Co-developed-by: Christopher S. Hall <[email protected]>
> Signed-off-by: Christopher S. Hall <[email protected]>
> Signed-off-by: Lakshmi Sowjanya D <[email protected]>
> ---
> include/linux/clocksource.h | 27 +++++++++++++++++++++++++
> include/linux/timekeeping.h | 2 ++
> kernel/time/timekeeping.c | 39 +++++++++++++++++++++++++++++++++++--
> 3 files changed, 66 insertions(+), 2 deletions(-)
>
[...]
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index b58dffc58a8f..4e5e931e766a 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1193,6 +1193,42 @@ static bool timestamp_in_interval(u64 start, u64 end,
> u64 ts)
> return false;
> }
>
> +static bool convert_clock(u64 *val, u32 numerator, u32 denominator)
> +{
> + u64 rem, res;
> +
> + if (!numerator || !denominator)
> + return false;
> +
> + res = div64_u64_rem(*val, denominator, &rem) * numerator;
> + *val = res + div_u64(rem * numerator, denominator);
> + return true;
> +}
> +
> +static bool convert_base_to_cs(struct system_counterval_t *scv)
> +{
> + struct clocksource *cs = tk_core.timekeeper.tkr_mono.clock;
> + struct clocksource_base *base = cs->base;
> + u32 num, den;
> +
> + /* The timestamp was taken from the time keeper clock source */
> + if (cs->id == scv->cs_id)
> + return true;
> +
> + /* Check whether cs_id matches the base clock */
> + if (!base || base->id != scv->cs_id)
> + return false;
> +
> + num = scv->use_nsecs ? cs->freq_khz : base->numerator;
> + den = scv->use_nsecs ? USEC_PER_SEC : base->denominator;
> +
> + if (!convert_clock(&scv->cycles, num, den))
> + return false;
> +
> + scv->cycles += base->offset;
> + return true;
> +}
> +
> /**
> * get_device_system_crosststamp - Synchronously capture system/device
> timestamp
> * @get_time_fn: Callback to get simultaneous device time and
> @@ -1238,8 +1274,7 @@ int get_device_system_crosststamp(int (*get_time_fn)
> * system counter value is the same as for the currently
> * installed timekeeper clocksource
> */
> - if (system_counterval.cs_id == CSID_GENERIC ||
> - tk->tkr_mono.clock->id != system_counterval.cs_id)
> + if (!convert_base_to_cs(&system_counterval))
> return -ENODEV;
AFAIU the error condition
system_counterval.cs_id == CSID_GENERIC
is silently dropped by this patch, but shouldn't be.
get_device_system_crosststamp() can only check the identity of a
clocksource (base) for non-generic ids.
Regards,
Peter
