RE: [PATCH v6 2/2] clocksource: Add Intel Keem Bay timer support

[Sanil, Shruthi]

> -----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?

Thanks,
Shruthi

> 
> Thanks,
> 
>         tglx