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

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Date:   Wed, 29 Apr 2020 18:19:18 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Johan Hovold <johan@...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

Hi Linus,

On Wed, Apr 29, 2020 at 02:12:24PM +0200, Linus Walleij wrote:
> On Tue, Apr 28, 2020 at 9:57 PM <mani@...nel.org> wrote:
> 
> > From: Manivannan Sadhasivam <mani@...nel.org>
> >
> > Add gpiochip support for Maxlinear/Exar USB to serial converter
> > for controlling the available gpios.
> >
> > Cc: Linus Walleij <linus.walleij@...aro.org>
> > Cc: linux-gpio@...r.kernel.org
> > Signed-off-by: Manivannan Sadhasivam <mani@...nel.org>
> 
> That's a nice and clean GPIO driver.

Thanks for the compliments :)

> 
> I would change this:
> 
>    port_priv->gc.label = "xr_gpios";
> 
> 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.
> 

Sounds reasonable. I can postfix the PID as below:

port_priv->gc.label = devm_kasprintf(port->dev, GFP_KERNEL, "XR%04x",
                                     port_priv->idProduct);

So this will become, "XR1410".

> Either way, it is not a super-big issue so:
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> 
> Is this a off-the-shelf product that can be bought or is it mainly
> integrated on boards?
> 

Both I believe, though I have only used it integrated in dev boards. But
a quick googling gives me below,

https://www.digikey.in/product-detail/en/maxlinear-inc/XR21V1410IL-0C-EB/1016-1425-ND/2636664

Thanks,
Mani

> I'm asking because I'm looking for a neat USB-to-serial adapter
> with some GPIOs (2 is enough) that can be used for reset and
> power cycling of lab boards using one simple piece of equipment.
> 
> Yours,
> Linus Walleij