PCI/DPC: Add "pcie_ports=dpc-native" to allow DPC without AER control

Prior to eed85ff4 ("PCI/DPC: Enable DPC only if AER is available"),
Linux handled DPC events regardless of whether firmware had granted it
ownership of AER or DPC, e.g., via _OSC.

PCIe r5.0, sec 6.2.10, recommends that the OS link control of DPC to
control of AER, so after eed85ff4, Linux handles DPC events only if it
has control of AER.

On platforms that do not grant OS control of AER via _OSC, Linux DPC
handling worked before eed85ff4 but not after.

To make Linux DPC handling work on those platforms the same way they did
before, add a "pcie_ports=dpc-native" kernel parameter that makes Linux
handle DPC events regardless of whether it has control of AER.

[bhelgaas: commit log, move pcie_ports_dpc_native to drivers/pci/]
Link: https://lore.kernel.org/r/20191023192205.97024-1-olof@lixom.netSigned-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -3540,6 +3540,8 @@
 			even if the platform doesn't give the OS permission to
 			use them.  This may cause conflicts if the platform
 			also tries to use these services.
+		dpc-native	Use native PCIe service for DPC only.  May
+				cause conflicts if firmware uses AER or DPC.
 		compat	Disable native PCIe services (PME, AER, DPC, PCIe
 			hotplug).
 

drivers/pci/pcie/dpc.c

@@ -291,7 +291,7 @@ static int dpc_probe(struct pcie_device *dev)
 	int status;
 	u16 ctl, cap;
 
-	if (pcie_aer_get_firmware_first(pdev))
+	if (pcie_aer_get_firmware_first(pdev) && !pcie_ports_dpc_native)
 		return -ENOTSUPP;
 
 	dpc = devm_kzalloc(device, sizeof(*dpc), GFP_KERNEL);

drivers/pci/pcie/portdrv.h

@@ -25,6 +25,8 @@
 
 #define PCIE_PORT_DEVICE_MAXSERVICES   5
 
+extern bool pcie_ports_dpc_native;
+
 #ifdef CONFIG_PCIEAER
 int pcie_aer_init(void);
 #else

drivers/pci/pcie/portdrv_core.c

@@ -250,8 +250,13 @@ static int get_port_device_capability(struct pci_dev *dev)
 		pcie_pme_interrupt_enable(dev, false);
 	}
 
+	/*
+	 * With dpc-native, allow Linux to use DPC even if it doesn't have
+	 * permission to use AER.
+	 */
 	if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
-	    pci_aer_available() && services & PCIE_PORT_SERVICE_AER)
+	    pci_aer_available() &&
+	    (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER)))
 		services |= PCIE_PORT_SERVICE_DPC;
 
 	if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||

drivers/pci/pcie/portdrv_pci.c

@@ -29,12 +29,20 @@ bool pcie_ports_disabled;
  */
 bool pcie_ports_native;
 
+/*
+ * If the user specified "pcie_ports=dpc-native", use the Linux DPC PCIe
+ * service even if the platform hasn't given us permission.
+ */
+bool pcie_ports_dpc_native;
+
 static int __init pcie_port_setup(char *str)
 {
 	if (!strncmp(str, "compat", 6))
 		pcie_ports_disabled = true;
 	else if (!strncmp(str, "native", 6))
 		pcie_ports_native = true;
+	else if (!strncmp(str, "dpc-native", 10))
+		pcie_ports_dpc_native = true;
 
 	return 1;
 }