linux-kernel - Re: [Xen-devel] [PATCHv1] x86: rtc_cmos platform device requires legacy irqs

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Date:	Thu, 3 Dec 2015 15:06:03 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, <xen-devel@...ts.xenproject.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCHv1] x86: rtc_cmos platform device requires
 legacy irqs

On 03/12/15 11:23, Vitaly Kuznetsov wrote:
> David Vrabel <david.vrabel@...rix.com> writes:
> 
>> Adding the rtc platform device when there are no legacy irqs (no
>> legacy PIC)
> 
> No PIC != No legacy IRQs, Hyper-V Gen2 represents such a platform (and
> it has RTC on irq8). I've tested this patch against it and it appears to
> work because the device is present in ACPI and we initialize it in
> drivers/acpi/acpi_cmos_rtc.c, add_rtc_cmos() bails out in the very
> beginning as we see PNP0b00 device.

It's not a legacy IRQ if it isn't going via the legacy PIC, it just
happens to have the same number.

I think it is safe to assume that any machine with a CMOS RTC but no PNP
information is also going to have a legacy PIC.

David
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