Hi Linus,

On Sat, Jan 4, 2020 at 1:38 AM Linus Walleij [off-list ref] wrote:

Sorry for slowness... christmas.

Np. Happy New Year!

On Thu, Dec 12, 2019 at 4:24 PM Geert Uytterhoeven [off-list ref] wrote:

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On Thu, Dec 12, 2019 at 3:34 PM Linus Walleij [off-list ref] wrote:

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+         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

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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.

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+           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