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 16:46:26 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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 11/16/2015 04:39 PM, Thomas Gleixner wrote:
> 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?

Of course. Thanks.

-boris
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