linux-kernel - Re: Time: new clocksource

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Message-ID: <a5192a80-0401-78fd-6fb3-e58a3b5a3923@linaro.org>
Date:   Mon, 6 Dec 2021 07:29:32 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Muni Sekhar <munisekharrms@...il.com>
Cc:     tglx@...utronix.de, LKML <linux-kernel@...r.kernel.org>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>
Subject: Re: Time: new clocksource

On 06/12/2021 07:00, Muni Sekhar wrote:
> On Sat, Dec 4, 2021 at 3:18 AM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>>
>> Hi Sekhar,
>>
>> On 03/12/2021 17:50, Muni Sekhar wrote:
>>> Hi All,
>>>
>>> We have a Digital PLL with 64 bit timer counter hardware and the
>>> counter is accessible from the CPU over the PCIe bus.
>>>
>>> Is it possible to add this timer counter hardware as new clocksource
>>> driver? To do this, can someone please point me to the existing
>>> reference source code(or patch) for this task.
>>
>> You can refer to the drivers located in drivers/clocksource
> I don't see the option in menuconfig to build the clocksource driver
> as a loadable kernel module, for example CONFIG_X86_PM_TIMER=m instead
> of CONFIG_X86_PM_TIMER=y.
> So a clocksource driver should always be part of the kernel built-in
> module?

Yes, that is the case today.

> If so, what's the reason for that?

The timer is a component needed at boot time, so a module version does
really not make sense.

So I would return back the question : what is the reason for a module?


>> git annotate on one of the driver can give you the initial commit where
>> recent submissions explain the timer internals.
>>
>>> Suppose if it is possible to add a new clocksource driver for this
>>> hardware then does any userspace get_timestamp* API would get the time
>>> from this new hardware?
>>
>> It should if the timer is selected as the clocksource
>>
>>
>> --
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> 
> 
> 


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