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

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Date:   Mon, 25 May 2020 13:12:03 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Johan Hovold <johan@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.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 Mon, May 25, 2020 at 10:59:59AM +0200, Linus Walleij wrote:
> 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.

Which is why they could use libudev :)

thanks,

greg k-h