Subject: Re: [PATCH] sparse_irq aka dyn_irq v13
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Yinghai Lu <yinghai@kernel.org>, Andrew Morton <akpm@linux-foundation.org>,
       mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org,
       travis@sgi.com
In-Reply-To: <4920B3E3.4050707@zytor.com>
References: <491434FB.2050904@kernel.org> <20081107124957.GA21709@elte.hu>
	 <49168BD3.5010204@kernel.org> <20081109073813.GA17180@elte.hu>
	 <86802c440811090003g5ac53822y852a4c1096228f8b@mail.gmail.com>
	 <20081110094033.GL22392@elte.hu>
	 <20081110015511.453a801e.akpm@linux-foundation.org>
	 <4918065A.6050402@kernel.org> <20081110100329.GA19970@elte.hu>
	 <491A9F87.8040403@kernel.org> <20081112120814.GG11352@elte.hu>
	 <491C8B38.9060901@kernel.org>
	 <20081113131850.d94fb229.akpm@linux-foundation.org>
	 <1226869137.7178.175.camel@pasglop> <4920B069.5020203@kernel.org>
	 <4920B15E.6090200@zytor.com> <4920B2A4.4040900@kernel.org>
	 <4920B3E3.4050707@zytor.com>
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Date: Mon, 17 Nov 2008 15:25:33 +1100
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On Sun, 2008-11-16 at 15:59 -0800, H. Peter Anvin wrote:
> 
> No, I think the whole notion of a static *numeric* identifier for an IRQ
> when it's something like MSI-X is simply pointless.  I think we should
> assign IRQ numbers beyond the legacy range dynamically.

Yup, exactly. Which is what we do on other platforms :-)

I think there is some value in getting rid of the irq_desc static array,
and to a certain extend having the ability to have irq_desc's be per-cpu
allocated but I think that patch tries to mix up way too many different
things, including a dubious attempt at tying the interrupt subsystem
into a specific implementation choice of x86 platforms for numbering.

Linux interrupts should just be a dynamically allocated number space,
with an exception for the 16 first ones (0 = illegal, 1...15 = legacy)
and that should be -separate- from the actual HW number of one on a
given PIC. In fact, powerpc handles multiple HW interrupt domain numbers
just fine that way which is very useful for embedded platforms with
funky cascaded PIC setups..
 
Ben.


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