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

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Date:   Wed, 8 Feb 2023 23:22:40 +0100
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        walter.chang@...iatek.com,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        John Stultz <jstultz@...gle.com>
Cc:     wsd_upstream@...iatek.com, stanley.chu@...iatek.com,
        Chun-hung.Wu@...iatek.com, Freddy.Hsin@...iatek.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 1/3] time/sched_clock: Export sched_clock_register()



On 08/02/2023 20:45, Krzysztof Kozlowski wrote:
> On 08/02/2023 20:41, 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.
> 
> ... and actually test if the system works fine when booted from such
> clocksource as a module. I have doubts that and unfortunately folks
> working on GKI like to put whatever stuff from mainline into modules
> even if it does not make sense for us (see long time ago discussion
> about pinctrl drivers).
> 

Yes thinking about it twice, it makes only sense if  the Arm architecture timer 
is running. Otherwise the system will hang on boot. I know that older MediaTek 
devices had problems with that...