PCI/MSI: Deal with devices lying about their MSI mask capability

It appears that some devices are lying about their mask capability,
pretending that they don't have it, while they actually do.
The net result is that now that we don't enable MSIs on such
endpoint.

Add a new per-device flag to deal with this. Further patches will
make use of it, sadly.

Signed-off-by: Marc Zyngier <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Cc: Bjorn Helgaas <[e-mail]>

drivers/pci/msi.c

···
 		goto out;
 
 	pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &control);
+	/* Lies, damned lies, and MSIs */
+	if (dev->dev_flags & PCI_DEV_FLAGS_HAS_MSI_MASKING)
+		control |= PCI_MSI_FLAGS_MASKBIT;
 
 	entry->msi_attrib.is_msix	= 0;
 	entry->msi_attrib.is_64		= !!(control & PCI_MSI_FLAGS_64BIT);

include/linux/pci.h

···
 	PCI_DEV_FLAGS_NO_FLR_RESET = (__force pci_dev_flags_t) (1 << 10),
 	/* Don't use Relaxed Ordering for TLPs directed at this device */
 	PCI_DEV_FLAGS_NO_RELAXED_ORDERING = (__force pci_dev_flags_t) (1 << 11),
+	/* Device does honor MSI masking despite saying otherwise */
+	PCI_DEV_FLAGS_HAS_MSI_MASKING = (__force pci_dev_flags_t) (1 << 12),
 };
 
 enum pci_irq_reroute_variant {