Subject: Re: [PATCH v2] x86/irq: Probe for PIC presence before allocating
 descs for legacy IRQs
To: Thomas Gleixner <tglx@linutronix.de>
References: <1446543614-3621-1-git-send-email-vkuznets@redhat.com>
 <564A43F5.30602@oracle.com> <alpine.DEB.2.11.1511162229520.3761@nanos>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>, x86@kernel.org,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Jiang Liu <jiang.liu@linux.intel.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>, linux-kernel@vger.kernel.org,
        xen-devel <xen-devel@lists.xen.org>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <564A4EB2.6050401@oracle.com>
Date: Mon, 16 Nov 2015 16:46:26 -0500
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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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