PCI: Add ACS Redirect disable quirk for Intel Sunrise Point

Intel Sunrise Point PCH hardware has an implementation of the ACS bits that
does not comply with the PCIe standard.  Add a device-specific quirk,
pci_quirk_disable_intel_spt_pch_acs_redir() to disable ACS Redirection on
this system.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
[bhelgaas: changelog, split to separate patch]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>

drivers/pci/quirks.c

@@ -4553,6 +4553,30 @@ static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
 	return 0;
 }
 
+static int pci_quirk_disable_intel_spt_pch_acs_redir(struct pci_dev *dev)
+{
+	int pos;
+	u32 cap, ctrl;
+
+	if (!pci_quirk_intel_spt_pch_acs_match(dev))
+		return -ENOTTY;
+
+	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
+	if (!pos)
+		return -ENOTTY;
+
+	pci_read_config_dword(dev, pos + PCI_ACS_CAP, &cap);
+	pci_read_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, &ctrl);
+
+	ctrl &= ~(PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC);
+
+	pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);
+
+	pci_info(dev, "Intel SPT PCH root port workaround: disabled ACS redirect\n");
+
+	return 0;
+}
+
 static const struct pci_dev_acs_ops {
 	u16 vendor;
 	u16 device;
@@ -4564,6 +4588,7 @@ static const struct pci_dev_acs_ops {
 	},
 	{ PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
 	    .enable_acs = pci_quirk_enable_intel_spt_pch_acs,
+	    .disable_acs_redir = pci_quirk_disable_intel_spt_pch_acs_redir,
 	},
 };