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+ The PCI Express Port Bus Driver Guide HOWTO
+ Tom L Nguyen
+ 11/03/2004
+1. About this guide
+This guide describes the basics of the PCI Express Port Bus driver
+and provides information on how to enable the service drivers to
+register/unregister with the PCI Express Port Bus Driver.
+2. Copyright 2004 Intel Corporation
+3. What is the PCI Express Port Bus Driver
+A PCI Express Port is a logical PCI-PCI Bridge structure. There
+are two types of PCI Express Port: the Root Port and the Switch
+Port. The Root Port originates a PCI Express link from a PCI Express
+Root Complex and the Switch Port connects PCI Express links to
+internal logical PCI buses. The Switch Port, which has its secondary
+bus representing the switch's internal routing logic, is called the
+switch's Upstream Port. The switch's Downstream Port is bridging from
+switch's internal routing bus to a bus representing the downstream
+PCI Express link from the PCI Express Switch.
+A PCI Express Port can provide up to four distinct functions,
+referred to in this document as services, depending on its port type.
+PCI Express Port's services include native hotplug support (HP),
+power management event support (PME), advanced error reporting
+support (AER), and virtual channel support (VC). These services may
+be handled by a single complex driver or be individually distributed
+and handled by corresponding service drivers.
+4. Why use the PCI Express Port Bus Driver?
+In existing Linux kernels, the Linux Device Driver Model allows a
+physical device to be handled by only a single driver. The PCI
+Express Port is a PCI-PCI Bridge device with multiple distinct
+services. To maintain a clean and simple solution each service
+may have its own software service driver. In this case several
+service drivers will compete for a single PCI-PCI Bridge device.
+For example, if the PCI Express Root Port native hotplug service
+driver is loaded first, it claims a PCI-PCI Bridge Root Port. The
+kernel therefore does not load other service drivers for that Root
+Port. In other words, it is impossible to have multiple service
+drivers load and run on a PCI-PCI Bridge device simultaneously
+using the current driver model.
+To enable multiple service drivers running simultaneously requires
+having a PCI Express Port Bus driver, which manages all populated
+PCI Express Ports and distributes all provided service requests
+to the corresponding service drivers as required. Some key
+advantages of using the PCI Express Port Bus driver are listed below:
+ - Allow multiple service drivers to run simultaneously on
+ a PCI-PCI Bridge Port device.
+ - Allow service drivers implemented in an independent
+ staged approach.
+ - Allow one service driver to run on multiple PCI-PCI Bridge
+ Port devices.
+ - Manage and distribute resources of a PCI-PCI Bridge Port
+ device to requested service drivers.
+5. Configuring the PCI Express Port Bus Driver vs. Service Drivers
+5.1 Including the PCI Express Port Bus Driver Support into the Kernel
+Including the PCI Express Port Bus driver depends on whether the PCI
+Express support is included in the kernel config. The kernel will
+automatically include the PCI Express Port Bus driver as a kernel
+driver when the PCI Express support is enabled in the kernel.
+5.2 Enabling Service Driver Support
+PCI device drivers are implemented based on Linux Device Driver Model.
+All service drivers are PCI device drivers. As discussed above, it is
+impossible to load any service driver once the kernel has loaded the
+PCI Express Port Bus Driver. To meet the PCI Express Port Bus Driver
+Model requires some minimal changes on existing service drivers that
+imposes no impact on the functionality of existing service drivers.
+A service driver is required to use the two APIs shown below to
+register its service with the PCI Express Port Bus driver (see
+section 5.2.1 & 5.2.2). It is important that a service driver
+initializes the pcie_port_service_driver data structure, included in
+header file /include/linux/pcieport_if.h, before calling these APIs.
+Failure to do so will result an identity mismatch, which prevents
+the PCI Express Port Bus driver from loading a service driver.
+5.2.1 pcie_port_service_register
+int pcie_port_service_register(struct pcie_port_service_driver *new)
+This API replaces the Linux Driver Model's pci_module_init API. A
+service driver should always calls pcie_port_service_register at
+module init. Note that after service driver being loaded, calls
+such as pci_enable_device(dev) and pci_set_master(dev) are no longer
+necessary since these calls are executed by the PCI Port Bus driver.
+5.2.2 pcie_port_service_unregister
+void pcie_port_service_unregister(struct pcie_port_service_driver *new)
+pcie_port_service_unregister replaces the Linux Driver Model's
+pci_unregister_driver. It's always called by service driver when a
+module exits.
+5.2.3 Sample Code
+Below is sample service driver code to initialize the port service
+driver data structure.
+static struct pcie_port_service_id service_id[] = { {
+ .vendor = PCI_ANY_ID,
+ .device = PCI_ANY_ID,
+ .port_type = PCIE_RC_PORT,
+ .service_type = PCIE_PORT_SERVICE_AER,
+ }, { /* end: all zeroes */ }
+static struct pcie_port_service_driver root_aerdrv = {
+ .name = (char *)device_name,
+ .id_table = &service_id[0],
+ .probe = aerdrv_load,
+ .remove = aerdrv_unload,
+ .suspend = aerdrv_suspend,
+ .resume = aerdrv_resume,
+Below is a sample code for registering/unregistering a service
+static int __init aerdrv_service_init(void)
+ int retval = 0;
+ retval = pcie_port_service_register(&root_aerdrv);
+ if (!retval) {
+ /*
+ * FIX ME
+ */
+ }
+ return retval;
+static void __exit aerdrv_service_exit(void)
+ pcie_port_service_unregister(&root_aerdrv);
+6. Possible Resource Conflicts
+Since all service drivers of a PCI-PCI Bridge Port device are
+allowed to run simultaneously, below lists a few of possible resource
+conflicts with proposed solutions.
+6.1 MSI Vector Resource
+The MSI capability structure enables a device software driver to call
+pci_enable_msi to request MSI based interrupts. Once MSI interrupts
+are enabled on a device, it stays in this mode until a device driver
+calls pci_disable_msi to disable MSI interrupts and revert back to
+INTx emulation mode. Since service drivers of the same PCI-PCI Bridge
+port share the same physical device, if an individual service driver
+calls pci_enable_msi/pci_disable_msi it may result unpredictable
+behavior. For example, two service drivers run simultaneously on the
+same physical Root Port. Both service drivers call pci_enable_msi to
+request MSI based interrupts. A service driver may not know whether
+any other service drivers have run on this Root Port. If either one
+of them calls pci_disable_msi, it puts the other service driver
+in a wrong interrupt mode.
+To avoid this situation all service drivers are not permitted to
+switch interrupt mode on its device. The PCI Express Port Bus driver
+is responsible for determining the interrupt mode and this should be
+transparent to service drivers. Service drivers need to know only
+the vector IRQ assigned to the field irq of struct pcie_device, which
+is passed in when the PCI Express Port Bus driver probes each service
+driver. Service drivers should use (struct pcie_device*)dev->irq to
+call request_irq/free_irq. In addition, the interrupt mode is stored
+in the field interrupt_mode of struct pcie_device.
+6.2 MSI-X Vector Resources
+Similar to the MSI a device driver for an MSI-X capable device can
+call pci_enable_msix to request MSI-X interrupts. All service drivers
+are not permitted to switch interrupt mode on its device. The PCI
+Express Port Bus driver is responsible for determining the interrupt
+mode and this should be transparent to service drivers. Any attempt
+by service driver to call pci_enable_msix/pci_disable_msix may
+result unpredictable behavior. Service drivers should use
+(struct pcie_device*)dev->irq and call request_irq/free_irq.
+6.3 PCI Memory/IO Mapped Regions
+Service drivers for PCI Express Power Management (PME), Advanced
+Error Reporting (AER), Hot-Plug (HP) and Virtual Channel (VC) access
+PCI configuration space on the PCI Express port. In all cases the
+registers accessed are independent of each other. This patch assumes
+that all service drivers will be well behaved and not overwrite
+other service driver's configuration settings.
+6.4 PCI Config Registers
+Each service driver runs its PCI config operations on its own
+capability structure except the PCI Express capability structure, in
+which Root Control register and Device Control register are shared
+between PME and AER. This patch assumes that all service drivers
+will be well behaved and not overwrite other service driver's
+configuration settings.