PCI: Enable SERR# forwarding for all bridges

task #29600094

commit b4f6dcb9d35688392d668c46e834f72c55900b49 upstream.
Backport summary: for 4.19 kernel ICX PCIe Gen4 support.

As per Figure 6-3 in PCIe r4.0, sec 6.2.6, ERR_ messages will be forwarded
from the secondary interface to the primary interface, if the SERR# Enable
bit in the Bridge Control register is set.

It seems clear that an ACPI hotplug parameter method (_HPP or _HPX) that
tells us to "enable SERR in the command register" (ACPI v6.2, sec 6.2.8,
6.2.9.1) refers to PCI_COMMAND_SERR, which enables reporting of errors by
the function itself.

For bridges, we also interpreted that to mean we should enable
PCI_BRIDGE_CTL_SERR, which enables *forwarding* of errors by the bridge.
But we didn't enable PCI_BRIDGE_CTL_SERR anywhere else, which means we
never enabled it for non-ACPI systems or ACPI systems that didn't supply
hotplug parameters.

That means errors reported below bridges were often never forwarded up to a
Root Port where they could be signaled via AER.

Enable PCI_BRIDGE_CTL_SERR for all bridges so we can get better error
reporting for downstream devices.
Signed-off-by: NBharat Kumar Gogada <bharat.kumar.gogada@xilinx.com>
[bhelgaas: changelog]
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
(cherry picked from commit b4f6dcb9d35688392d668c46e834f72c55900b49)
Signed-off-by: NEthan Zhao <haifeng.zhao@intel.com>
Signed-off-by: NArtie Ding <artie.ding@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>

drivers/pci/probe.c

@@ -1829,8 +1829,6 @@ static void program_hpp_type0(struct pci_dev *dev, struct hpp_type0 *hpp)
 		pci_write_config_byte(dev, PCI_SEC_LATENCY_TIMER,
 				      hpp->latency_timer);
 		pci_read_config_word(dev, PCI_BRIDGE_CONTROL, &pci_bctl);
-		if (hpp->enable_serr)
-			pci_bctl |= PCI_BRIDGE_CTL_SERR;
 		if (hpp->enable_perr)
 			pci_bctl |= PCI_BRIDGE_CTL_PARITY;
 		pci_write_config_word(dev, PCI_BRIDGE_CONTROL, pci_bctl);
@@ -2112,6 +2110,24 @@ static void pci_configure_eetlp_prefix(struct pci_dev *dev)
 #endif
 }
 
+static void pci_configure_serr(struct pci_dev *dev)
+{
+	u16 control;
+
+	if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
+
+		/*
+		 * A bridge will not forward ERR_ messages coming from an
+		 * endpoint unless SERR# forwarding is enabled.
+		 */
+		pci_read_config_word(dev, PCI_BRIDGE_CONTROL, &control);
+		if (!(control & PCI_BRIDGE_CTL_SERR)) {
+			control |= PCI_BRIDGE_CTL_SERR;
+			pci_write_config_word(dev, PCI_BRIDGE_CONTROL, control);
+		}
+	}
+}
+
 static void pci_configure_device(struct pci_dev *dev)
 {
 	struct hotplug_params hpp;
@@ -2122,6 +2138,7 @@ static void pci_configure_device(struct pci_dev *dev)
 	pci_configure_relaxed_ordering(dev);
 	pci_configure_ltr(dev);
 	pci_configure_eetlp_prefix(dev);
+	pci_configure_serr(dev);
 
 	memset(&hpp, 0, sizeof(hpp));
 	ret = pci_get_hp_params(dev, &hpp);