[PATCH] PCI: fixup PCI_INTERRUPT_LINE for VMD downstream devices

[Nirmal Patel <nirmal.patel@linux.intel.com>]

VMD does not support legacy interrupts for devices downstream from a
VMD endpoint. So initialize the PCI_INTERRUPT_LINE to 0 for these
devices to ensure we don't try to set up a legacy irq for them.

Note: This patch was proposed by Jim, I am trying to upstream it.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Signed-off-by: Nirmal Patel <nirmal.patel@linux.intel.com>
---
 arch/x86/pci/fixup.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
index b33afb240601..a3b34a256e7f 100644
--- a/arch/x86/pci/fixup.c
+++ b/arch/x86/pci/fixup.c
@@ -653,6 +653,20 @@ static void quirk_no_aersid(struct pci_dev *pdev)
 DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
 			      PCI_CLASS_BRIDGE_PCI, 8, quirk_no_aersid);
 
+#if IS_ENABLED(CONFIG_VMD)
+/* 
+ * VMD does not support legacy interrupts for downstream devices.
+ * So PCI_INTERRPUT_LINE needs to be initialized to 0 to ensure OS
+ * doesn't try to configure a legacy irq.
+ */
+static void quirk_vmd_interrupt_line(struct pci_dev *dev)
+{
+	if (is_vmd(dev->bus))
+		pci_write_config_byte(dev, PCI_INTERRUPT_LINE, 0);
+}
+DECLARE_PCI_FIXUP_HEADER(PCI_ANY_ID, PCI_ANY_ID, quirk_vmd_interrupt_line);
+#endif
+
 static void quirk_intel_th_dnv(struct pci_dev *dev)
 {
 	struct resource *r = &dev->resource[4];
-- 
2.39.1