linux-kernel - Re: Userspace I/O driver core

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Date:	Sat, 16 Dec 2006 14:48:13 +0000
From:	"Dr. David Alan Gilbert" <linux@...blig.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Avi Kivity <avi@...o.co.il>, Greg KH <greg@...ah.com>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: Userspace I/O driver core

* Arjan van de Ven (arjan@...radead.org) wrote:
> 
> > I understand one still has to write a kernel driver to shut up the irq.  
> > How about writing a small bytecode interpreter to make event than 
> > unnecessary?
> 
> if you do that why not do a real driver.

Because perhaps it is potentially very simple - i.e.
if most of these drivers turn out to be:

if (*loc1 & mask)
{
   *loc2=value;
   flag we have an interrupt
}

then all you actually need to do is provide a way to
specify loc1, mask, loc2 and value.  You could provide
a small handful of mechanisms to suit most simple pieces of hardware
and also provide a definition for the hardware designers to say
'if you make your interrupt registers like this then the software
is dead easy'.  A bytecode interpreter seems a little overkill
unless you think that two or three levels of that type of test/mask
could cope with 90%+ of the cases.
There are probably lots of people reinventing the wheel for simple IO 
boards and the hardware guys will be making it up each time as well.

Dave
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    | Running GNU/Linux on Alpha,68K| Happy  \ 
\ gro.gilbert @ treblig.org | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/
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