X86 cannot store the irq domain pointer in struct device without breaking
XEN because the irq domain pointer takes precedence over arch_*_msi_irqs()
fallbacks.

XENs MSI teardown relies on default_teardown_msi_irqs() which invokes
arch_teardown_msi_irq(). default_teardown_msi_irqs() is a trivial iterator
over the msi entries associated to a device.

Implement this loop in xen_teardown_msi_irqs() to prepare for removal of
the fallbacks for X86.

This is a preparatory step to wrap XEN MSI alloc/free into a irq domain
which in turn allows to store the irq domain pointer in struct device and
to use the irq domain functions directly.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/pci/xen.c |   23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -376,20 +376,31 @@ static void xen_initdom_restore_msi_irqs
 static void xen_teardown_msi_irqs(struct pci_dev *dev)
 {
 	struct msi_desc *msidesc;
+	int i;
+
+	for_each_pci_msi_entry(msidesc, dev) {
+		if (msidesc->irq) {
+			for (i = 0; i < msidesc->nvec_used; i++)
+				xen_destroy_irq(msidesc->irq + i);
+		}
+	}
+}
+
+static void xen_pv_teardown_msi_irqs(struct pci_dev *dev)
+{
+	struct msi_desc *msidesc = first_pci_msi_entry(dev);
 
-	msidesc = first_pci_msi_entry(dev);
 	if (msidesc->msi_attrib.is_msix)
 		xen_pci_frontend_disable_msix(dev);
 	else
 		xen_pci_frontend_disable_msi(dev);
 
-	/* Free the IRQ's and the msidesc using the generic code. */
-	default_teardown_msi_irqs(dev);
+	xen_teardown_msi_irqs(dev);
 }
 
 static void xen_teardown_msi_irq(unsigned int irq)
 {
-	xen_destroy_irq(irq);
+	WARN_ON_ONCE(1);
 }
 
 #endif
@@ -412,7 +423,7 @@ int __init pci_xen_init(void)
 #ifdef CONFIG_PCI_MSI
 	x86_msi.setup_msi_irqs = xen_setup_msi_irqs;
 	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
-	x86_msi.teardown_msi_irqs = xen_teardown_msi_irqs;
+	x86_msi.teardown_msi_irqs = xen_pv_teardown_msi_irqs;
 	pci_msi_ignore_mask = 1;
 #endif
 	return 0;
@@ -436,6 +447,7 @@ static void __init xen_hvm_msi_init(void
 	}
 
 	x86_msi.setup_msi_irqs = xen_hvm_setup_msi_irqs;
+	x86_msi.teardown_msi_irqs = xen_teardown_msi_irqs;
 	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
 }
 #endif
@@ -472,6 +484,7 @@ int __init pci_xen_initial_domain(void)
 #ifdef CONFIG_PCI_MSI
 	x86_msi.setup_msi_irqs = xen_initdom_setup_msi_irqs;
 	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
+	x86_msi.teardown_msi_irqs = xen_teardown_msi_irqs;
 	x86_msi.restore_msi_irqs = xen_initdom_restore_msi_irqs;
 	pci_msi_ignore_mask = 1;
 #endif