linux-kernel - Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features

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Message-ID: <CACRpkdbQ-o0NOLzQK3Jb06wx2u62ik2xv1Q8UNpN_SMmGhgVXg@mail.gmail.com>
Date:   Fri, 7 Feb 2020 18:17:26 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     christopher.s.hall@...el.com
Cc:     netdev <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        jacob.e.keller@...el.com,
        Richard Cochran <richardcochran@...il.com>,
        "David S. Miller" <davem@...emloft.net>, sean.v.kelley@...el.com
Subject: Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO
 Driver with PHC interface changes to support additional H/W Features

On Fri, Jan 31, 2020 at 7:40 AM <christopher.s.hall@...el.com> wrote:

> The TGPIO hardware doesn't implement interrupts. For TGPIO input, the
> output edge-timestamp API is re-used to implement a user-space polling
> interface.

It you modeled it reusing the GPIO subsystem (which I don't know if
you can) you would get access to the gpiochip character device
/dev/gpiochipN and be able to read timestamped events like
the tool in tools/gpio/gpio-event-mon.c does.

That said I am still confused about what this driver does or what the
purpose is.

GPIO pins in or out? Network coming in or going out using PTP?

What is the use case?

Yours,
Linus Walleij