PCI: add infrastructure for devices with broken INTx masking

pci_intx_mask_supported() assumes INTx masking is supported if the
PCI_COMMAND_INTX_DISABLE bit is writable.  But when that bit is set,
some devices don't actually mask INTx or update PCI_STATUS_INTERRUPT
as we expect.

This patch adds a way for quirks to identify these broken devices.

[bhelgaas: split out from Chelsio quirk addition]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -2876,6 +2876,9 @@ bool pci_intx_mask_supported(struct pci_dev *dev)
 	bool mask_supported = false;
 	u16 orig, new;
 
+	if (dev->broken_intx_masking)
+		return false;
+
 	pci_cfg_access_lock(dev);
 
 	pci_read_config_word(dev, PCI_COMMAND, &orig);

drivers/pci/quirks.c

@@ -2929,6 +2929,16 @@ static void __devinit disable_igfx_irq(struct pci_dev *dev)
 DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x0102, disable_igfx_irq);
 DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL, 0x010a, disable_igfx_irq);
 
+/*
+ * Some devices may pass our check in pci_intx_mask_supported if
+ * PCI_COMMAND_INTX_DISABLE works though they actually do not properly
+ * support this feature.
+ */
+static void __devinit quirk_broken_intx_masking(struct pci_dev *dev)
+{
+	dev->broken_intx_masking = 1;
+}
+
 static void pci_do_fixups(struct pci_dev *dev, struct pci_fixup *f,
 			  struct pci_fixup *end)
 {

include/linux/pci.h

@@ -324,6 +324,7 @@ struct pci_dev {
 	unsigned int    is_hotplug_bridge:1;
 	unsigned int    __aer_firmware_first_valid:1;
 	unsigned int	__aer_firmware_first:1;
+	unsigned int	broken_intx_masking:1;
 	pci_dev_flags_t dev_flags;
 	atomic_t	enable_cnt;	/* pci_enable_device has been called */