linux-kernel - Re: [PATCH] lp: implement proper detach function for parport

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Message-ID: <20130619183231.GA7684@kroah.com>
Date:	Wed, 19 Jun 2013 11:32:31 -0700
From:	Greg Kroah-Hartman <greg@...ah.com>
To:	Hannes Weisbach <hannes_weisbach@....net>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lp: implement proper detach function for parport_driver
 lp

On Wed, Jun 19, 2013 at 07:04:51PM +0200, Hannes Weisbach wrote:
> >> Signed-off-by: Hannes Weisbach <hannes_weisbach@....net>
> >> ---
> >> Granted, for normal parport drivers this is usually not an issue,
> >> because the device does not go away. However, I am currently writing a
> >> Linux device driver for a USB to parallel port converter [0] and
> >> therefore need proper detaching. Additionally, the wrong ref count
> >> keeps me from simply rmmod my driver and insmod a new version while
> >> developing and testing.
> > 
> > Really?  We already have a usb to parallel port driver in the kernel
> > tree that seems to work just fine.
> 
> >  It's been there since the 2.3 kernel
> > days, so either it has the same problem, or your driver is doing
> > something odd.
> 
> Do you mean the USB Printer class driver for pseudo parallel port
> adapters?  They don't use the char/lp.c printer driver.  (Or I didn't
> see it).  I'm writing a driver for USB2LPT [0], which gives you a real
> /dev/parportN-device in user space, with which you can do all the
> bit-twiddling like with a real parallel port.
> 
> Or do you mean USS720 (misc/uss720.c) and MOS7715 (serial/mos7720.c)
> drivers.

Yes, I mean these.

> They are doing what I am doing: translating whatever the
> user does on a /dev/parportN-node and sending device-specific commands
> over USB.  When they do parport_announce_port(), lp.c should also be
> initialized and they should have the same problem.

Why hasn't anyone reported that problem then?  Surely someone must use
these, they've been in the kernel tree for over a decade now.

> On second thought, my patch might not be optimal.  lp.c stores
> instance-structs in an array of size 8.  So after 8 re-plugs, lp.c
> will not instantiate any more printer devices.  I think I better go
> all the way and replace that array with a list, to have a proper
> solution.

Proper solutions are always good :)

thanks,

greg k-h
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