linux-kernel - Re: [PATCH v5 2/3] usb: serial: xr

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Date:   Sat, 5 Dec 2020 23:21:09 +0100
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,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Angelo Dureghello <angelo.dureghello@...esys.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v5 2/3] usb: serial: xr_serial: Add gpiochip support

On Tue, Dec 1, 2020 at 4:50 PM Johan Hovold <johan@...nel.org> wrote:
> On Tue, Dec 01, 2020 at 03:37:38PM +0100, Linus Walleij wrote:
> > On Sun, Nov 22, 2020 at 6:08 PM Manivannan Sadhasivam <mani@...nel.org> wrote:

> > You know the names of the pins...
> >
> > > +       port_priv->gc.ngpio = 6;
> > > +       port_priv->gc.label = "xr_gpios";
> > > +       port_priv->gc.request = xr_gpio_request;
> > > +       port_priv->gc.free = xr_gpio_free;
> > > +       port_priv->gc.get_direction = xr_gpio_direction_get;
> > > +       port_priv->gc.direction_input = xr_gpio_direction_input;
> > > +       port_priv->gc.direction_output = xr_gpio_direction_output;
> > > +       port_priv->gc.get = xr_gpio_get;
> > > +       port_priv->gc.set = xr_gpio_set;
> > > +       port_priv->gc.owner = THIS_MODULE;
> > > +       port_priv->gc.parent = &port->dev;
> > > +       port_priv->gc.base = -1;
> > > +       port_priv->gc.can_sleep = true;
> >
> > So assign port_priv->gc.names here as well with an array
> > of strings with the names ("RI", "CD", ... etc).
> > This makes it look really nice in userspace if you do
> > e.g. "lsgpio".
>
> Last time we tried that gpiolib still used a flat namespace so that you
> can't have have more than one device using the same names. Unless that
> has changed this is a no-go. See
>
>         https://lore.kernel.org/r/20180930122703.7115-1-johan@kernel.org
>
> for our previous discussion about this.

Hm hm yeah we actually put in a nasty warning there since:

                gpio = gpio_name_to_desc(gc->names[i]);
                if (gpio)
                        dev_warn(&gdev->dev,
                                 "Detected name collision for GPIO name '%s'\n",
                                 gc->names[i]);


A better approach might be to create an array of names
prepended with something device-unique like the USB
bus topology? Or do we need a helper to help naming the
GPIOs? What would be helpful here?

name = kasprintf(GFP_KERNEL, "%s-NAME", topology_str);

Yours,
Linus Walleij