linux-kernel - Re: [PATCH] char/pcmcia: add scr24x

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Message-ID: <7482716.OJg3IkqZRp@wuerfel>
Date:   Mon, 17 Oct 2016 13:34:54 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Lubomir Rintel <lkundrak@...sk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH] char/pcmcia: add scr24x_cs chip card interface driver

On Monday, October 17, 2016 1:22:01 PM CEST Lubomir Rintel wrote:
> > > > And why do you need a char device for this type of
> > > > hardware?  Isn't there already an existing interface for this device
> > > > class?
> > > 
> > > (Arnd answered this better than I would do in his response to this
> > > message).
> > 
> > Yeah, that makes sense.  A bit messy though.
> 
> I guess that makes sense; the chip card readers tend to be rather
> complex and the API (IFD Handler API) user space typically uses is
> rather generic -- it would require quite some logic to interface with a
> particular hardware.
> 
> Moreover, most of the present-day smart card readers are standard CCID
> class USB devices, with the CCID to IFD done in userspace. There's some
> serial readers too, attached via UARTs too that use the tty ioctls to
> detect the card presence and set the baud rate, etc.
> 
> The rest (PCMCIA) seem to emulate either of the two. It still makes
> sense to implement the IFD in userspace and I guess there's not too
> much common ground for a device class here.

Well, you could in theory implement this as a tty driver
and be compatible with the serial port devices, see
drivers/tty/goldfish.c for an example driver.

Not sure if that actually improves things for you or not,
but the advantage is that there is an existing kernel
subsystem for it.

	Arnd