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

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Message-ID: <87mvtr7p2s.fsf@vitty.brq.redhat.com>
Date:	Thu, 03 Dec 2015 12:23:55 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	David Vrabel <david.vrabel@...rix.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

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.

> causes a conflict with other devices that end up using the
> same irq number.
>
> In a single VCPU Xen PV guest we should have:
>
> /proc/interrupts:
>            CPU0
>   0:       4934  xen-percpu-virq      timer0
>   1:          0  xen-percpu-ipi       spinlock0
>   2:          0  xen-percpu-ipi       resched0
>   3:          0  xen-percpu-ipi       callfunc0
>   4:          0  xen-percpu-virq      debug0
>   5:          0  xen-percpu-ipi       callfuncsingle0
>   6:          0  xen-percpu-ipi       irqwork0
>   7:        321   xen-dyn-event     xenbus
>   8:         90   xen-dyn-event     hvc_console
>   ...
>
> But hvc_console cannot get its interrupt because it is already in use
> by rtc0 and the console does not work.
>
>   genirq: Flags mismatch irq 8. 00000000 (hvc_console) vs. 00000000 (rtc0)
>
> The rtc_cmos device requires a particular legacy irq so don't add it
> if there are no legacy irqs.
>
> Reported-by: Sander Eikelenboom <linux@...elenboom.it>
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> Tested-by: Sander Eikelenboom <linux@...elenboom.it>
> ---
>  arch/x86/kernel/rtc.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
> index cd96852..07c70f1 100644
> --- a/arch/x86/kernel/rtc.c
> +++ b/arch/x86/kernel/rtc.c
> @@ -14,6 +14,7 @@
>  #include <asm/time.h>
>  #include <asm/intel-mid.h>
>  #include <asm/rtc.h>
> +#include <asm/i8259.h>
>
>  #ifdef CONFIG_X86_32
>  /*
> @@ -200,6 +201,10 @@ static __init int add_rtc_cmos(void)
>  	}
>  #endif
>
> +	/* RTC uses legacy IRQs. */
> +	if (!nr_legacy_irqs())
> +		return -ENODEV;
> +
>  	platform_device_register(&rtc_device);
>  	dev_info(&rtc_device.dev,
>  		 "registered platform RTC device (no PNP device found)\n");

-- 
  Vitaly
--
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