linux-kernel - Re: [PATCH 6/8] Kconfig: no userspace I/O on s390.

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Date:	Sun, 13 May 2007 02:35:58 -0700
From:	Greg KH <gregkh@...e.de>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 6/8] Kconfig: no userspace I/O on s390.

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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