> -----Original Message-----
> From: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> Sent: Thursday, December 23, 2021 7:46 PM
> To: Sanil, Shruthi <shruthi.sanil@xxxxxxxxx>; Thomas Gleixner
> <tglx@xxxxxxxxxxxxx>; robh+dt@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx
> Cc: andriy.shevchenko@xxxxxxxxxxxxxxx; kris.pan@xxxxxxxxxxxxxxx;
> mgross@xxxxxxxxxxxxxxx; Thokala, Srikanth <srikanth.thokala@xxxxxxxxx>;
> Raja Subramanian, Lakshmi Bai <lakshmi.bai.raja.subramanian@xxxxxxxxx>;
> Sangannavar, Mallikarjunappa <mallikarjunappa.sangannavar@xxxxxxxxx>
> Subject: Re: [PATCH v6 2/2] clocksource: Add Intel Keem Bay timer support
>
> On 11/11/2021 11:42, Sanil, Shruthi wrote:
> >> -----Original Message-----
> >> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >> Sent: Monday, September 27, 2021 3:11 AM
> >> To: Sanil, Shruthi <shruthi.sanil@xxxxxxxxx>;
> >> daniel.lezcano@xxxxxxxxxx;
> >> robh+dt@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> >> devicetree@xxxxxxxxxxxxxxx
> >> Cc: andriy.shevchenko@xxxxxxxxxxxxxxx; kris.pan@xxxxxxxxxxxxxxx;
> >> mgross@xxxxxxxxxxxxxxx; Thokala, Srikanth
> >> <srikanth.thokala@xxxxxxxxx>; Raja Subramanian, Lakshmi Bai
> >> <lakshmi.bai.raja.subramanian@xxxxxxxxx>;
> >> Sangannavar, Mallikarjunappa
> <mallikarjunappa.sangannavar@xxxxxxxxx>;
> >> Sanil, Shruthi <shruthi.sanil@xxxxxxxxx>
> >> Subject: Re: [PATCH v6 2/2] clocksource: Add Intel Keem Bay timer
> >> support
> >>
> >> On Tue, Sep 07 2021 at 00:06, shruthi sanil wrote:
> >>> +
> >>> +/* Provides a unique ID for each timer */ static
> >>> +DEFINE_IDA(keembay_timer_ida);
> >>
> >>> +
> >>> + timer_id = ida_alloc(&keembay_timer_ida, GFP_KERNEL);
> >>> + if (timer_id < 0) {
> >>> + ret = timer_id;
> >>> + goto err_keembay_ce_to_free;
> >>> + }
> >>
> >> May I ask what the purpose of the IDA, which is backed by a full
> >> blown xarray, is here?
> >>
> >> AFAICT all you want is a unique number for the timer name for up to 8
> >> timers.
> >>
> >>> + timer_name = kasprintf(GFP_KERNEL, "keembay_timer%d",
> >> timer_id);
> >>
> >> So what's wrong about:
> >>
> >> static unsigned int keembay_timer_id;
> >>
> >> timer_name = kasprintf(GFP_KERNEL, "keembay_timer%d",
> >> keembay_timer_id++);
> >>
> >> Hmm?
> >
> > Yes, we had initially implemented it in the similar way, but in the
> > course of review it got changed to use IDA.
> >
> >>
> >>> +
> >>> + clockevents_config_and_register(&keembay_ce_to->clkevt,
> >>> + timer_of_rate(keembay_ce_to),
> >>> + 1,
> >>> + U32_MAX);
> >>
> >> Aside of that what's the point of registering more than one of those
> >> timers as clock event? The core will only use one and the rest is
> >> just going to use memory for no value.
> >
> > Instead of
> > keembay_ce_to->clkevt.cpumask = cpumask_of(0); can I update it as
> > keembay_ce_to->clkevt.cpumask = cpu_possible_mask; so that each timer
> > would be associated with different cores?
>
> Let me try to clarify:
>
> The Intel Keem bay Soc is a 4 x Cortex-A53
>
> The arch ARM timer is per CPU on this platform.
>
> Case 1:
> -------
> - the architected timer is not desired and this timer is wanted to be used
> instead (but rating tells the opposite) => rewrite per cpu code
>
> Case 2:
> -------
> - the architected timer are desired and this timer is used as a broadcast
> timer when a core is going done with cpuidle. One timer is needed.
>
> - In order to prevent useless wakeup, the timer uses the flag DYNIRQ.
> However, cpumask_of(0) is set and makes inoperative this flag. In order to
> make full use of it, clkevt.cpumask must be cpu_possible_mask
>
> Hope that helps
>
> -- Daniel
>
Thank You Daniel for the explanation.
In case of KMB, we are using the ARM architecture timer.
We would be using the timer for case2. So I need to register Just 1 timer.
I'll check and make the changes accordingly and submit the next patch.
Thank You!
Regards,
Shruthi
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