linux-kernel - Re: [PATCH] x86/dt: use linear irq domain for ioapic(s).

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Date:	Wed, 8 Aug 2012 14:07:37 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Grant Likely <grant.likely@...retlab.ca>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/dt: use linear irq domain for ioapic(s).

On Wed, Aug 08, 2012 at 01:51:36PM +0200, Sebastian Andrzej Siewior wrote:
> On 08/08/2012 12:46 PM, Thierry Reding wrote:
> >On another note, I saw that you've used the "intel,ce4100" prefix in
> >various places and I wonder if it would be useful to replace them with
> >something more generic like "intel,hpet", "intel,lapic" and
> >"intel,ioapic" respectively. The hardware that I use is based on an Atom
> >N450 and works with the current code, so it really isn't ce4100-
> >specific.
> 
> No. You do have a compatible entry. It first appeared on the ce4100
> CPU. If it happens to also work on the n450 then it seems to be
> compatible with that one. "This" is documented somewhere…
> Usually you add 'compatible = "your cpu", "generic binding"' in case
> you need a fixup / errata whatever for "your cpu". Even if you compare
> all hpets from Intel there is the one or other difference / errata.

Exactly, but "ce4100-hpet" isn't very generic. What I'm saying is that
the last entry in the compatible list should be something generic, like
"intel,hpet", which can be overridden by putting a more specific entry
in front. I'd expect the ce4100 HPET to use something like this:

	compatible = "intel,ce4100-hpet", "intel,hpet";

On N450 this could for instance be:

	compatible = "intel,n450-hpet", "intel,hpet";

With that in place, the driver code can match on "intel,hpet" to catch
all implementations and use the more specific entries if quirks are
required for the specific hardware.

Thierry

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