[PATCH] PCI: Fix pcibios_update_irq misuse of irq number

pcibios_update_irq writes an irq number into the config space
of a given PCI device, but ignores the fact that this number
is a virtual interrupt number, which might be a very different
value from what the underlying hardware is using.

The obvious fix is to fetch the HW interrupt number from the
corresponding irq_data structure. This is slightly complicated
by the fact that this interrupt might be services by a stacked
domain.

This has been tested on KVM with kvmtool.

Reported-by: Lorenzo Pieralisi <redacted>
Tested-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Marc Zyngier <redacted>
---
 drivers/pci/setup-irq.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/setup-irq.c b/drivers/pci/setup-irq.c
index 4e2d595..828cbc9 100644
--- a/drivers/pci/setup-irq.c
+++ b/drivers/pci/setup-irq.c

@@ -15,11 +15,19 @@
 #include <linux/errno.h>
 #include <linux/ioport.h>
 #include <linux/cache.h>
+#include <linux/irq.h>
 
 void __weak pcibios_update_irq(struct pci_dev *dev, int irq)
 {
-	dev_dbg(&dev->dev, "assigning IRQ %02d\n", irq);
-	pci_write_config_byte(dev, PCI_INTERRUPT_LINE, irq);
+	struct irq_data *d;
+
+	d = irq_get_irq_data(irq);
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+	while (d->parent_data)
+		d = d->parent_data;
+#endif
+	dev_dbg(&dev->dev, "assigning IRQ %02ld\n", d->hwirq);
+	pci_write_config_byte(dev, PCI_INTERRUPT_LINE, d->hwirq);
 }