linux-kernel - Re: [PATCH 2/2] usb: serial: xr

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Date:   Mon, 25 May 2020 10:59:59 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Manivannan Sadhasivam <mani@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-usb <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        patong.mxl@...il.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 2/2] usb: serial: xr_serial: Add gpiochip support

On Tue, May 19, 2020 at 10:57 AM Johan Hovold <johan@...nel.org> wrote:
> > On Wed, Apr 29, 2020 at 02:12:24PM +0200, Linus Walleij wrote:

> > > to something that is device-unique, like "xr-gpios-<serial number>"
> > > which makes it easy to locate the GPIOs on a specific serial converter
> > > for lab use. However the USB serial maintainers know better what
> > > to use here. Whatever makes a USB-to-serial unique from a TTY
> > > point of view is probably fine with me too.
> > >
> > > My idea is that people might want to know which USB cable
> > > this is sitting on, so I have this USB cable and from this label
> > > I can always figure out which GPIO device it is.
>
> I think we've had this discussion before. First, not every device has a
> unique serial number. Second, we already have a universal way of
> distinguishing devices namely by using the bus topology. That's
> available through sysfs and shouldn't have to be be re-encoded by every
> driver in the gpiochip name.

I remember I even referred to this myself, but I've been waning a bit
on it recently, because it turns out that userspace/users aren't very
good at parsing sysfs for topology.

For userspace other than udev there seems to be a kind of agreement
gap. Dunno how best to bridge it though. Education maybe.

Yours,
Linus Walleij