RE: [PATCH v7 01/12] timekeeping: Add base clock properties in clocksource structure

["D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@xxxxxxxxx>]

> -----Original Message-----
> From: Peter Hilber <peter.hilber@xxxxxxxxxxxxxxx>
> Sent: Tuesday, April 30, 2024 7:58 PM
> To: D, Lakshmi Sowjanya <lakshmi.sowjanya.d@xxxxxxxxx>;
> tglx@xxxxxxxxxxxxx; jstultz@xxxxxxxxxx; giometti@xxxxxxxxxxxx;
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> intel-wired-lan@xxxxxxxxxxxxxxxx; andriy.shevchenko@xxxxxxxxxxxxxxx; Dong,
> Eddie <eddie.dong@xxxxxxxxx>; Hall, Christopher S
> <christopher.s.hall@xxxxxxxxx>; Brandeburg, Jesse
> <jesse.brandeburg@xxxxxxxxx>; davem@xxxxxxxxxxxxx;
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> mcoquelin.stm32@xxxxxxxxx; perex@xxxxxxxx; linux-
> sound@xxxxxxxxxxxxxxx; Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>;
> N, Pandith <pandith.n@xxxxxxxxx>; Mohan, Subramanian
> <subramanian.mohan@xxxxxxxxx>; T R, Thejesh Reddy
> <thejesh.reddy.t.r@xxxxxxxxx>
> Subject: Re: [PATCH v7 01/12] timekeeping: Add base clock properties in
> clocksource structure
> 
> On 30.04.24 10:52, lakshmi.sowjanya.d@xxxxxxxxx wrote:
> > From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
> >
> > 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 <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Co-developed-by: Christopher S. Hall <christopher.s.hall@xxxxxxxxx>
> > Signed-off-by: Christopher S. Hall <christopher.s.hall@xxxxxxxxx>
> > Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
> > ---
> >  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

Thanks Peter,
Noted. The check will be added as below:

if (system_counterval.cs_id == CSID_GENERIC ||
                         !convert_base_to_cs(&system_counterval))

Regards,
Sowjanya