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

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Date:	Thu, 3 Dec 2015 10:43:24 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	<x86@...nel.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCHv1] x86: rtc_cmos platform device requires legacy irqs

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.

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");
-- 
2.1.4

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