linux-kernel - Re: [PATCH 1/3] resource: shared I/O region support

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Message-ID: <20100402132912.4d2af552@jbarnes-piketon>
Date:	Fri, 2 Apr 2010 13:29:12 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Giel van Schijndel <me@...tis.eu>,
	Hans de Goede <hdegoede@...hat.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Jonathan Cameron <jic23@....ac.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Laurens Leemans <laurens@...nips.com>,
	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] resource: shared I/O region support

On Mon, 29 Mar 2010 19:29:57 +0100
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > Well that does keep it simple, and with just one user that's probably
> > best.
> > 
> > But why not use the common bus driver method?  Muxing at the resource
> > level only seems to solve part of the problem...  It doesn't guarantee
> > for example that driver A does something to a shared region that breaks
> > driver B; it just makes sure they don't access the same region at the
> > same time.
> 
> The obvious reason for not doing that kind of grand over-engineering is
> that you are assuming the devices involved are remotely related. On quite
> a few systems we have a collection of superio config interfaces on random
> low ports all with their own lock/unlock rituals. They range from
> parallel devices to watchdogs and god knows what else. Right now we have
> various bits of driver code (parport is a good one) that exist on a cross
> fingers, pray and poke model. It would be nice to fix that.
> 
> For most super I/O devices the muxing is basically a glorified chip select
> line. There isn't any structure to impose over it. Where you have
> structure there are better ways to do it, but one does not exclude the
> other.

Well I'm not sure such over-engineering would be "grand", but it does
seem like overkill for the devices you're covering here.  At any rate,
the patch is in my linux-next tree, so it'll head to Linus next merge
cycle unless some big new objections arise.

-- 
Jesse Barnes, Intel Open Source Technology Center
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