linux-kernel - Re: [PATCH] USB: ftdi

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Date:	Fri, 13 Jun 2014 11:31:57 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Sascha Silbe <x-linux@...ra-silbe.de>,
	Johan Hovold <jhovold@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: ftdi_sio: add GPIO support

On Fri, Jun 13, 2014 at 09:25:07AM +0200, Linus Walleij wrote:
> On Mon, Jun 9, 2014 at 3:21 PM, Sascha Silbe <x-linux@...ra-silbe.de> wrote:
> 
> > The chips can operate either in regular or in bitbang mode. Care was
> > taken to prevent using GPIOs if the serial device is in use and vice
> > versa.
> 
> Very interesting patch! I've seen USB-based GPIO things before
> but never a dual-mode thing.
> 
> There was already a comment to move the implementation to a
> separate file, which I won't repeat.
> 
> But I also want to bring the device model into question: normally
> when a mother device spawns children across different subsystems
> we model them as MFD devices (drivers/mfd) that instantiate
> children for the different subsystems. So you could spawn a
> serial and a GPIO device from a USB-based hub device there.
> 
> I do not know if that is really apropriate in this case. It seems the
> device is first and foremost FTDI.
> 
> But it could still spawn a child platform device for the GPIO stuff
> so that this can live as a separate driver under drivers/gpio/gpio-ftdi.c
> or similar.
> 
> You could then use something like:
> 
> struct platform_device *gdev;

Ick, no, it's a USB device, do not abuse the platform_device code any
more than it currently is (note, I HATE the platform device code,
someday I'll delete it entirely...  Well, I can dream...)

greg k-h
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