MIME-Version: 1.0
References: <CAHhAz+jpmksehY4BSH9jJPYuY+jykSHtx9TNiG-gAkq10zaXSQ@mail.gmail.com>
 <fe9dbf81-e060-36ab-b769-215af3d65ba7@linaro.org>
In-Reply-To: <fe9dbf81-e060-36ab-b769-215af3d65ba7@linaro.org>
From:   Muni Sekhar <munisekharrms@gmail.com>
Date:   Mon, 6 Dec 2021 11:30:21 +0530
Message-ID: <CAHhAz+iEQTtfxXB8sNEL4WxFjUZo5LYTo4EVyH0mT2=NH3VaUA@mail.gmail.com>
Subject: Re: Time: new clocksource
To:     Daniel Lezcano <daniel.lezcano@linaro.org>
Cc:     tglx@linutronix.de, LKML <linux-kernel@vger.kernel.org>,
        kernelnewbies <kernelnewbies@kernelnewbies.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Sat, Dec 4, 2021 at 3:18 AM Daniel Lezcano <daniel.lezcano@linaro.org> w=
rote:
>
> 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=3Dm instead
of CONFIG_X86_PM_TIMER=3Dy.
So a clocksource driver should always be part of the kernel built-in
module? If so, what's the reason for that?

>
> 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
>
>
> --
> <http://www.linaro.org/> Linaro.org =E2=94=82 Open source software for AR=
M SoCs
>
> Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
> <http://twitter.com/#!/linaroorg> Twitter |
> <http://www.linaro.org/linaro-blog/> Blog


--=20
Thanks,
Sekhar