Date: Sun, 13 May 2007 02:35:58 -0700
From: Greg KH <gregkh@suse.de>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Greg KH <greg@kroah.com>, linux-kernel@vger.kernel.org,
       linux-s390@vger.kernel.org, akpm@linux-foundation.org
Subject: Re: [PATCH 6/8] Kconfig: no userspace I/O on s390.
Message-ID: <20070513093558.GA11317@suse.de>
References: <20070420113430.GG3738@skybase> <20070503053047.GB7458@kroah.com> <1178181374.32267.17.camel@localhost>
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On Thu, May 03, 2007 at 10:36:14AM +0200, Martin Schwidefsky wrote:
> On Wed, 2007-05-02 at 22:30 -0700, Greg KH wrote:
> > > Hide the config menu for userspace I/O on s390.
> > 
> > Why?  Who says s390 can't have userspace I/O drivers someday?
> 
> Theoretically yes, but in practice this is very unlikely to happen. Some
> reasons why:
> 1) There are only very few device drivers for s390, the few we need
> we'll do as kernel space drivers
> 2) The irq abstraction of uio is awkward. The irq handler uses a 32-bit
> integer. On s390 each ccw device has it's own irq and ccw devices are
> identified with a string "x.y.zzzz". Then there are devices that deliver
> external interrupts where a 16-bit number is used to identify the
> source. You could invent some mapping logic of a 32 bit integer to all
> the possible interrupt sources but it doesn't really match.
> 3) s390 doesn't use memory mapped i/o, you always need to execute a
> privileged instruction to trigger activity on the device, e.g. ssch for
> a ccw device, siga for qdio, nqap for crypto, ...
> 
> So I have my doubts that we will ever see a uio driver for s390. If we
> do we can unhide the config menu again.

Ok, that's find, can you bounce me the patch that made this change
again?

thanks,

greg k-h
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