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

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Date:	Fri, 4 Dec 2015 14:06:06 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>, <x86@...nel.org>
CC:	<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>,
	"Vitaly Kuznetsov" <vkuznets@...hat.com>
Subject: Re: [Xen-devel] [PATCHv1] x86: rtc_cmos platform device requires
 legacy irqs

On 03/12/15 10:43, David Vrabel wrote:
> Adding the rtc platform device when there are no legacy irqs (no
> legacy PIC) causes a conflict with other devices that end up using the
> same irq number.

An alternative is to remove the rtc_cmos platform device in Xen PV
guests.

Any preference on how this regression should be fixed?

David

8<--------------------------
x86: Xen PV guests don't have the rtc_cmos platform device

Adding the rtc platform device in a Xen PV guests causes an IRQ
conflict because these guests do not have a legacy PIC.

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)

So don't add the rtc_cmos device in Xen PV guests.

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 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index cd96852..7b190b8 100644
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -200,6 +200,9 @@ static __init int add_rtc_cmos(void)
 	}
 #endif
 
+	if (xen_pv_domain())
+		return -ENODEV;
+
 	platform_device_register(&rtc_device);
 	dev_info(&rtc_device.dev,
 		 "registered platform RTC device (no PNP device found)\n");
-- 
2.1.4

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