[PATCH v2 1/2] pci: Fix flaw in pci_acs_enabled()

[Alex Williamson <alex.williamson@redhat.com>]

Downstream ports support for all ACS flags supercedes multifunction
exclusion of some flags.  The PCIe spec also fully specifies which
PCIe types are subject to the multifunction rules and excludes event
collectors and PCIe-to-PCI bridges entirely.  Document each rule to
the section of the PCIe spec.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/pci/pci.c |   59 ++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 45 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b099e00..457ae51 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2354,6 +2354,19 @@ void pci_enable_acs(struct pci_dev *dev)
 	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
 }
 
+static bool pci_acs_flags_enabled(struct pci_dev *pdev, u16 acs_flags)
+{
+	int pos;
+	u16 ctrl;
+
+	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ACS);
+	if (!pos)
+		return false;
+
+	pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);
+	return (ctrl & acs_flags) == acs_flags;
+}
+
 /**
  * pci_acs_enabled - test ACS against required flags for a given device
  * @pdev: device to test
@@ -2364,8 +2377,7 @@ void pci_enable_acs(struct pci_dev *dev)
  */
 bool pci_acs_enabled(struct pci_dev *pdev, u16 acs_flags)
 {
-	int pos, ret;
-	u16 ctrl;
+	int ret;
 
 	ret = pci_dev_specific_acs_enabled(pdev, acs_flags);
 	if (ret >= 0)
@@ -2374,23 +2386,42 @@ bool pci_acs_enabled(struct pci_dev *pdev, u16 acs_flags)
 	if (!pci_is_pcie(pdev))
 		return false;
 
-	/* Filter out flags not applicable to multifunction */
-	if (pdev->multifunction)
+	switch (pci_pcie_type(pdev)) {
+	/*
+	 * PCIe 3.0, 6.12.1 excludes ACS on these devices.  "Not applicable"
+	 */
+	case PCI_EXP_TYPE_PCI_BRIDGE:
+	case PCI_EXP_TYPE_RC_EC:
+		break;
+	/*
+	 * PCIe 3.0, 6.12.1.1 specifies full ACS capabilities on downstream
+	 * ports, regardless of them being multifunction devices.
+	 */
+	case PCI_EXP_TYPE_DOWNSTREAM:
+	case PCI_EXP_TYPE_ROOT_PORT:
+		return pci_acs_flags_enabled(pdev, acs_flags);
+	/*
+	 * PCIe 3.0, 6.12.1.2 specifies unimplemented ACS capabilities on
+	 * multifunction devices.  6.12 footnote identifies specifically
+	 * which devices types this applies to.
+	 */
+	case PCI_EXP_TYPE_ENDPOINT:
+	case PCI_EXP_TYPE_UPSTREAM:
+	case PCI_EXP_TYPE_LEG_END:
+	case PCI_EXP_TYPE_RC_END:
+		if (!pdev->multifunction)
+			break;
+
 		acs_flags &= (PCI_ACS_RR | PCI_ACS_CR |
 			      PCI_ACS_EC | PCI_ACS_DT);
 
-	if (pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM ||
-	    pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT ||
-	    pdev->multifunction) {
-		pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ACS);
-		if (!pos)
-			return false;
-
-		pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);
-		if ((ctrl & acs_flags) != acs_flags)
-			return false;
+		return pci_acs_flags_enabled(pdev, acs_flags);
 	}
 
+	/*
+	 * PCIe 3.0, 6.12.1.3 specifies no ACS capabilties are applicable
+	 * to single function devices with the exception of downstream ports.
+	 */
 	return true;
 }