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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Harish Jenny K N <harish_kandiga@mentor.com>,
	Eugeniu Rosca <erosca@de.adit-jv.com>,
	Alexander Graf <graf@amazon.com>,
	Peter Maydell <peter.maydell@linaro.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Phil Reid <preid@electromag.com.au>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	Magnus Damm <magnus.damm@gmail.com>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [PATCH v3 5/7] gpio: Add GPIO Aggregator/Repeater driver
Date: Mon, 6 Jan 2020 09:23:08 +0100
Message-ID: <CAMuHMdUGGcjoX8TDDS5qGLtJZxizUK=BpasSQK3t1K-dhEgZCg@mail.gmail.com> (raw)
In-Reply-To: <CACRpkda8QD_tDA=YVDRNVnHd8QHs-yHBTzZuJHsnocgMdxv9cA@mail.gmail.com>

Hi Linus,

On Sat, Jan 4, 2020 at 1:38 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> Sorry for slowness... christmas.

Np. Happy New Year!

> On Thu, Dec 12, 2019 at 4:24 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Thu, Dec 12, 2019 at 3:34 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> > > > +         This can serve the following purposes:
> > > > +           1. Assign a collection of GPIOs to a user, or export them to a
> > > > +              virtual machine,
> > >
> > > This is ambiguous. What is a "user"? A process calling from
> > > userspace? A device tree node?
> >
> > A user is an entity with a UID, typically listed in /etc/passwd.
> > This is similar to letting some, not all, people on the machine access
> > the CD-ROM drive.
>
> Ah I get it. Maybe we can say "assign permissions for a collection
> of GPIOs to a user".

OK

> > > I would write "assign a collection of GPIO lines from any lines on
> > > existing physical GPIO chips to form a new virtual GPIO chip"
> > >
> > > That should be to the point, right?
> >
> > Yes, that's WHAT it does. The WHY is the granular access control.
>
> So I guess we can write both?

OK.

> > > > +           3. Provide a generic driver for a GPIO-operated device, to be
> > > > +               controlled from userspace using the GPIO chardev interface.
> > >
> > > I don't understand this, it needs to be elaborated. What is meant
> > > by a "GPIO-operated device" in this context? Example?
> >
> > E.g. a motor. Or a door opener.
> >
> >         door-opener {
> >                 compatible = "mydoor,opener";
> >
> >                 gpios = <&gpio2 19 GPIO_ACTIVE_HIGH>;
> >         };
> >
> > You don't need a full-featured kernel driver for that, so just bind the
> > gpio-aggregator to the door-opener, and control it through libgpiod.
>
> Yep it's a perfect industrial control example, I get it.
>
> Maybe we should blurb something about industrial control?

OK.

> The rest I think we cleared out else I will see it when I review again.

The remaining discussion point is "GPIO Repeater in Device Tree", i.e.
the GPIO inverter usecase, which might be solved better by adding a
GPIO_INVERTED flag.

Shall I rip that out, incorporate review comments, and report?

Thanks!



--
Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-27  8:42 [PATCH v3 0/7] gpio: Add GPIO Aggregator/Repeater Geert Uytterhoeven
2019-11-27  8:42 ` [PATCH v3 1/7] gpiolib: Add GPIOCHIP_NAME definition Geert Uytterhoeven
2019-11-28  3:38   ` Ulrich Hecht
2019-12-02 21:17   ` Eugeniu Rosca
2019-12-12 10:37   ` Linus Walleij
2019-11-27  8:42 ` [PATCH v3 2/7] gpiolib: Add support for gpiochipN-based table lookup Geert Uytterhoeven
2019-11-28  3:38   ` Ulrich Hecht
2019-12-12 13:20   ` Linus Walleij
2019-12-12 13:33     ` Geert Uytterhoeven
2019-12-12 14:36       ` Linus Walleij
2019-11-27  8:42 ` [PATCH v3 3/7] gpiolib: Add support for GPIO line " Geert Uytterhoeven
2019-11-28  3:39   ` Ulrich Hecht
2019-12-12 13:40   ` Linus Walleij
2019-11-27  8:42 ` [PATCH v3 4/7] dt-bindings: gpio: Add gpio-repeater bindings Geert Uytterhoeven
2019-11-28  3:39   ` Ulrich Hecht
2019-12-03  5:51   ` Harish Jenny K N
2019-12-05 21:06   ` Rob Herring
2019-12-06  9:17     ` Geert Uytterhoeven
2019-12-06 15:03       ` Rob Herring
2020-01-06  8:12         ` Geert Uytterhoeven
2020-01-07  9:22           ` Harish Jenny K N
2020-01-16  5:09             ` Harish Jenny K N
2019-11-27  8:42 ` [PATCH v3 5/7] gpio: Add GPIO Aggregator/Repeater driver Geert Uytterhoeven
2019-11-27 14:15   ` Eugeniu Rosca
2019-11-27 14:33     ` Geert Uytterhoeven
2019-11-28  3:40   ` Ulrich Hecht
2019-12-03  5:42   ` Harish Jenny K N
2019-12-03  8:17     ` Geert Uytterhoeven
2019-12-03  8:51       ` Harish Jenny K N
2019-12-03 10:51   ` Eugeniu Rosca
2020-01-09 13:35     ` Geert Uytterhoeven
2020-01-09 13:49       ` Eugeniu Rosca
2019-12-12 14:34   ` Linus Walleij
2019-12-12 15:24     ` Geert Uytterhoeven
2020-01-04  0:38       ` Linus Walleij
2020-01-06  8:23         ` Geert Uytterhoeven [this message]
2020-01-08 23:12           ` Linus Walleij
2019-11-27  8:42 ` [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation Geert Uytterhoeven
2019-11-28  3:41   ` Ulrich Hecht
2019-12-12 14:42   ` Linus Walleij
2019-12-12 14:48     ` Geert Uytterhoeven
2020-01-04  0:21       ` Linus Walleij
2020-01-06  8:06         ` Geert Uytterhoeven
2019-11-27  8:42 ` [PATCH v3 7/7] MAINTAINERS: Add GPIO Aggregator/Repeater section Geert Uytterhoeven
2019-12-03  5:38   ` Harish Jenny K N
2020-01-18  1:46 ` [PATCH v3 0/7] gpio: Add GPIO Aggregator/Repeater Eugeniu Rosca
2020-01-20  9:33   ` Geert Uytterhoeven
2020-01-20 12:14     ` Eugeniu Rosca

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