linux-kernel - Re: [PATCH 1/3] time/sched_clock: Export sched_clock

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Date:   Fri, 10 Feb 2023 10:08:03 +0000
From:   Walter Chang (張維哲) 
        <Walter.Chang@...iatek.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "krzysztof.kozlowski@...aro.org" <krzysztof.kozlowski@...aro.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "jstultz@...gle.com" <jstultz@...gle.com>,
        "macro@...am.me.uk" <macro@...am.me.uk>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stanley Chu (朱原陞) 
        <stanley.chu@...iatek.com>,
        Freddy Hsin (辛恒豐) 
        <Freddy.Hsin@...iatek.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Chun-Hung Wu (巫駿宏) 
        <Chun-hung.Wu@...iatek.com>
Subject: Re: [PATCH 1/3] time/sched_clock: Export sched_clock_register()

On Wed, 2023-02-08 at 20:41 +0100, Matthias Brugger wrote:
> 
> On 08/02/2023 15:24, Krzysztof Kozlowski wrote:
> > On 08/02/2023 10:48, walter.chang@...iatek.com wrote:
> > > From: Chun-Hung Wu <chun-hung.wu@...iatek.com>
> > > 
> > > clocksource driver may use sched_clock_register()
> > > to resigter itself as a sched_clock source.
> > > Export it to support building such driver
> > > as module, like timer-mediatek.c
> > > 
> > > Signed-off-by: Chun-Hung Wu <chun-hung.wu@...iatek.com>
> > > ---
> > >   kernel/time/sched_clock.c | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/kernel/time/sched_clock.c
> > > b/kernel/time/sched_clock.c
> > > index 8464c5acc913..8e49e87d1221 100644
> > > --- a/kernel/time/sched_clock.c
> > > +++ b/kernel/time/sched_clock.c
> > > @@ -150,8 +150,7 @@ static enum hrtimer_restart
> > > sched_clock_poll(struct hrtimer *hrt)
> > >   	return HRTIMER_RESTART;
> > >   }
> > >   
> > > -void __init
> > > -sched_clock_register(u64 (*read)(void), int bits, unsigned long
> > > rate)
> > > +void sched_clock_register(u64 (*read)(void), int bits, unsigned
> > > long rate)
> > 
> > Is there a non-init caller?
> > 
> > >   {
> > >   	u64 res, wrap, new_mask, new_epoch, cyc, ns;
> > >   	u32 new_mult, new_shift;
> > > @@ -223,6 +222,7 @@ sched_clock_register(u64 (*read)(void), int
> > > bits, unsigned long rate)
> > >   
> > >   	pr_debug("Registered %pS as sched_clock source\n",
> > > read);
> > >   }
> > > +EXPORT_SYMBOL_GPL(sched_clock_register);
> > 
> > Where is the module using it?
> > 
> > You need to bring users of these two changes, not just prepare
> > something
> > for your out of tree patches.
> > 
> 
> I'd propose to add at least one driver that will need these changes,
> to make it 
> clear why you need that.
> 
> Regards,
> Matthias

I have uploaded another patch to make timer-mediatek.c driver become
loadable module.


https://lore.kernel.org/lkml/20230210100058.19861-1-walter.chang@mediatek.com/T/#u

This driver registers an always-on timer as tick_broadcast_device 
on MediaTek SoCs. If the system does not load this module, system 
would also boot normally since Arm Generic Timer will take over 
this part.

Thanks,
Walter Chang