[PATCH] xen/pv: Add PV specific legacy_pic struct to expose legacy IRQs.

[Jennifer Herbert]

The ACPI tables doesn't always contain all IRQs for legacy devices
such as RTC.  Since no PIC controller is visible for a PV linux guest,
under Xen, legacy_pic currently defaults to the null_legacy_pic - with
reports no legacy IRQs.  Since the commit "rtc: cmos: Do not assume
irq 8 for rtc when there are no legacy irqs" by Hans de Goede
(commit id: a1e23a42f1bdc00e32fc4869caef12e4e6272f26), the rtc now
incorrectly decides it has no irq it can use, for some hardware.

This patch rectifies the problem by providing a xen legacy_pic
struct, which is much like the null_legacy_pic except that it
reports NR_IRQS_LEGACY irqs.

Signed-off-by: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>
---
 arch/x86/xen/enlighten_pv.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index c54a493..7644bdf 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -33,6 +33,7 @@
 #include <linux/gfp.h>
 #include <linux/edd.h>
 #include <linux/frame.h>
+#include <linux/irq.h>
 
 #include <xen/xen.h>
 #include <xen/events.h>
@@ -49,6 +50,7 @@
 #include <xen/acpi.h>
 
 #include <asm/paravirt.h>
+#include <asm/i8259.h>
 #include <asm/apic.h>
 #include <asm/page.h>
 #include <asm/xen/pci.h>
@@ -1188,6 +1190,41 @@ static void __init xen_dom0_set_legacy_features(void)
 	x86_platform.legacy.rtc = 1;
 }
 
+/*
+ * The ACPI tables doesn't always contain all IRQ's for legacy devices
+ * such as RTC.  Since no PIC controller is visible, we'd otherwise
+ * default to the null_legacy_pic - with no legacy IRQs.  To allow drivers
+ * to use these IRQs despite this, provide a xen specific legacy_pic
+ * structure, which is noop, other then reporting NR_IRQS_LEGACY irqs.
+ */
+
+static void xen_legacy_pic_noop(void) { };
+static void xen_legacy_pic_uint_noop(unsigned int unused) { };
+static void xen_legacy_pic_int_noop(int unused) { };
+static int xen_legacy_pic_irq_pending_noop(unsigned int irq)
+{
+	return 0;
+}
+
+static int xen_legacy_pic_probe(void)
+{
+	pr_info("Using Xen legacy PIC\n");
+	return nr_legacy_irqs();
+}
+
+struct legacy_pic xen_legacy_pic = {
+	.nr_legacy_irqs = NR_IRQS_LEGACY,
+	.chip = &dummy_irq_chip,
+	.mask = xen_legacy_pic_uint_noop,
+	.unmask = xen_legacy_pic_uint_noop,
+	.mask_all = xen_legacy_pic_noop,
+	.restore_mask = xen_legacy_pic_noop,
+	.init = xen_legacy_pic_int_noop,
+	.probe = xen_legacy_pic_probe,
+	.irq_pending = xen_legacy_pic_irq_pending_noop,
+	.make_irq = xen_legacy_pic_uint_noop,
+};
+
 /* First C function to be called on Xen boot */
 asmlinkage __visible void __init xen_start_kernel(void)
 {
@@ -1267,6 +1304,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
 
 	xen_init_capabilities();
 
+	legacy_pic = &xen_legacy_pic;
+
 #ifdef CONFIG_X86_LOCAL_APIC
 	/*
 	 * set up the basic apic ops.
-- 
1.8.3.1