PCI: Add ACS quirk for APM X-Gene devices

The APM X-Gene PCIe root port does not support ACS at this point. However,
the hardware provides isolation and source validation through the SMMU.
The stream ID generated by the PCIe ports contain both the bus/device/
function number as well as the port ID in its 3 most significant bits.
Turn on ACS but disable all the peer-to-peer features.

Signed-off-by: Feng Kan <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Alex Williamson <[e-mail]>
Acked-by: Tanmay Inamdar <[e-mail]>

drivers/pci/quirks.c

···
 	return acs_flags ? 0 : 1;
 }
 
+static int pci_quirk_xgene_acs(struct pci_dev *dev, u16 acs_flags)
+{
+	/*
+	 * X-Gene root matching this quirk do not allow peer-to-peer
+	 * transactions with others, allowing masking out these bits as if they
+	 * were unimplemented in the ACS capability.
+	 */
+	acs_flags &= ~(PCI_ACS_SV | PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF);
+
+	return acs_flags ? 0 : 1;
+}
+
 /*
  * Many Intel PCH root ports do provide ACS-like features to disable peer
  * transactions and validate bus numbers in requests, but do not provide an
···
 	{ 0x10df, 0x720, pci_quirk_mf_endpoint_acs }, /* Emulex Skyhawk-R */
 	/* Cavium ThunderX */
 	{ PCI_VENDOR_ID_CAVIUM, PCI_ANY_ID, pci_quirk_cavium_acs },
+	/* APM X-Gene */
+	{ PCI_VENDOR_ID_AMCC, 0xE004, pci_quirk_xgene_acs },
 	{ 0 }
 };