linux-kernel - Re: [RFC PATCH v1 08/20] kernel: time: Add system time to system counter translation

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Message-ID: <CACRpkdZMGcYW7HjKegKCn6yT=f88KQ5BZfA37iyfrzv2s1hsNA@mail.gmail.com>
Date:   Thu, 16 Sep 2021 23:48:36 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     "D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Saha, Tamal" <tamal.saha@...el.com>, bala.senthil@...el.com,
        Dipen Patel <dipenp@...dia.com>
Subject: Re: [RFC PATCH v1 08/20] kernel: time: Add system time to system
 counter translation

On Tue, Aug 24, 2021 at 6:48 PM <lakshmi.sowjanya.d@...el.com> wrote:

> From: Christopher Hall <christopher.s.hall@...el.com>
>
> The GPIOlib event generation interface supplies a time in terms of the
> realtime system clock. The driver must translate the system clock to
> something meaningful to the hardware.
>
> The Intel(R) PMC Timed I/O hardware uses ART to trigger events. For
> most Intel(R) platforms that use TSC for timekeeping this added
> function translates from system clock to TSC. The relation between TSC
> and ART is easily derived from CPUID[15H].
>
> Signed-off-by: Christopher Hall <christopher.s.hall@...el.com>
> Signed-off-by: Tamal Saha <tamal.saha@...el.com>
> Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> Reviewed-by: Mark Gross <mgross@...ux.intel.com>

I don't quite understand what this patch does, but it looks very generic.
I think the exact usecase needs to be in the commit message.

In either case, this is a patch TGLX et al needs to look at, we can't
merge timekeeping code without their consent.

Yours,
Linus Walleij