linux-kernel - Re: [PATCH v2] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs

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Date:	Mon, 16 Nov 2015 22:39:01 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:	Vitaly Kuznetsov <vkuznets@...hat.com>, x86@...nel.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	linux-kernel@...r.kernel.org, xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v2] x86/irq: Probe for PIC presence before allocating
 descs for legacy IRQs

On Mon, 16 Nov 2015, Boris Ostrovsky wrote:
> Xen expects legacy interrupts to be there (pretty much for the same reason as
> Hyper-V does) and with this change arch_probe_nr_irqs() returns zero and no
> descriptors are allocated.

Right, because everything which has a PIT gets them and everything
which does not have a PIT does not.

> We can allocate those descriptors as needed in xen_irq_init() (if we know that
> IRQs are legacy), although that would look somewhat ugly and out of place.

Why preallocating them in xen_irq_init()? You simply can remove the
NR_IRQS_LEGACY checks in xen_allocate_irq_gsi/xen_free_irq(), right?

Thanks,

	tglx
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