[PATCH] pci: do not try to assign irq 255

[Hannes Reinecke <hare@suse.de>]

The PCI config space reseves a byte for the interrupt line,
so irq 255 actually refers to 'not set'.
However, the 'irq' field for struct pci_dev is an integer,
so the original meaning is lost, causing the system to
assign an interrupt '255', which fails.

So we should _not_ assign an interrupt value here, and
allow upper layers to fixup things.

This patch make PCI devices with MSI interrupts only
(like the xhci device on certain HP laptops) work properly.

Cc: Frederik Himpe <fhimpe@vub.ac.be>
Cc: Oliver Neukum <oneukum@suse.de>
Cc: David Haerdeman <david@hardeman.nu>
Cc: linux-usb@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Signed-off-by: Hannes Reinecke <hare@suse.de>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 6186f03..a2db887f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -923,7 +923,8 @@ static void pci_read_irq(struct pci_dev *dev)
 	dev->pin = irq;
 	if (irq)
 		pci_read_config_byte(dev, PCI_INTERRUPT_LINE, &irq);
-	dev->irq = irq;
+	if (irq < 255)
+		dev->irq = irq;
 }
 
 void set_pcie_port_type(struct pci_dev *pdev)