Added pcie-howto.txt for describing the information on PCI Express basics and Root Complex driver. Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xxxxxxxxxx> --- Changes for v2: - Fixed comments from "Randy Dunlap" Documentation/PCI/00-INDEX | 2 + Documentation/PCI/pcie-howto.txt | 186 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 188 insertions(+) create mode 100644 Documentation/PCI/pcie-howto.txt diff --git a/Documentation/PCI/00-INDEX b/Documentation/PCI/00-INDEX index b8b7721..d61e7b9 100644 --- a/Documentation/PCI/00-INDEX +++ b/Documentation/PCI/00-INDEX @@ -6,6 +6,8 @@ pci-error-recovery.txt - Info on PCI error recovery MSI-HOWTO.txt - The Message Signaled Interrupts (MSI) Driver Guide HOWTO and FAQ +pcie-howto.txt + - A guide describing the PCI Express basics and Root Complex driver pcie-portbus-howto.txt - A guide describing the PCI Express Port Bus driver pcie-aer-howto.txt diff --git a/Documentation/PCI/pcie-howto.txt b/Documentation/PCI/pcie-howto.txt new file mode 100644 index 0000000..df464b5 --- /dev/null +++ b/Documentation/PCI/pcie-howto.txt @@ -0,0 +1,186 @@ + PCI Express HOWTO + Jagannadha Sutradharudu Teki <jagannadh.teki@xxxxxxxxx> + 12/12/2013 + +1. About this guide + +This guide describes the basics of the PCI Express bus and provides +information on what the Linux PCIe subsystem looks like and ends with +a brief description of PCI Host controller/Root complex driver along +with some sample code. + +2. Basic terminology and conventions + +PCI Express is +- A high performance IO interconnect for peripherals. +- Low hardware design overhead compared to PCI, as it uses less pins. +- A serial point-to-point interconnect between two devices. +- Implements packet-based protocol for data transfer. +- Supports features like Advanced power management, Advanced error + reporting facility, and hot-plug. + _________ + | | + | CPU | + |_________| + | + ___________________|___________________________ + | | ________ + | ROOT COMPLEX | | | + | |--------| Memory | + | Switch Port Root port | |________| + |_______________________________________________| + | PCIe Bus0 + ____________________________|______________________________________ + | | | + ____ ______|______ | ____|____ + | | / \ __|__ | | + | EP |-----| SWITCH | | | | BRIDGE | + |____| \_____________/ | EP | | PCIe - | + | | |_____| | PCI/PCIe| + __|__ __|__ |_________| + | | | | | PCIe Bus1 + | EP | | EP | __________|________________ + |_____| |_____| | | + __|__ __|__ + | | | | + | EP | | EP | + |_____| |_____| + +Root Complex (RC) +Connects the CPU and memory subsystem to the PCIe fabric (A topology comprised of PCIe +nodes like Root Complex, Endpoint, Bridge or a Switch) + +Port +Interface between a PCIe component and the Link. + +Link +PCIe interconnect is referred as a Link, and connects two devices. + +Lane +A PCIe link consists of either 1, 2, 4, 8, 12, 16 or 32 signals in each direction +(each signal needs two wires - one for Tx and other for Rx). These signals are +referred to as Lanes. + +Upstream Port +Port that points in the direction of RC. + +Downstream Port +Port that points away from the RC. + +Root Port +Whose upstream port is RC and dowstream port should be an EP or Bridge. + +Switch Port +Whose upstream port is RC and dowstream port is always a switch. + +Endpoint (EP) +Devices other than RC, Switches and Bridges which either generate or terminate a PCIe +transaction. These are peripheral devices such as Ethernet, USB and graphics devices. + +Switch +PCIe device single upstream port as RC and multiple downstream ports as EP's, +Switches or Bridges. + +Bridge +Is for extending PCIe Bus segment - whose downstream port points to one more PCIe bus. + +3. Linux PCIe Subsystem + + ifconfig open()/close/read()/write() /proc, /sys + ^ ^ ^ ^ + | | | | + | | | | + | | | V + | | | PCIe Port Bus services + | | | (AER, HP, PME, VC + | | | drivers/pci/pcie/ + | | | drivers/pci/hotplug) + V V V ^ + Socket Block Char | + layer Subsystem Subsystem | + ^ ^ ^ | pcie_port_service_register() + | | | | + | | | | + V V V V + Common net USB Input PCIe Port Core + device layer Core Core (drivers/pci/pcie/portdrv_core.c) + ^ ^ ^ ^ + | | | | pcie_port_bus_register() + | | | | + _____V_____ ____V____ ____V_____ _________V___________ + | | | | | | | | + All these are | GEM | | USB HC | | Mouse/KB/| | PCIe Port Bus driver| + PCI endpoint | Controller| | driver | | TS HC | | (drivers/pci/pcie/ | + drivers | driver | | | | driver | | portdrv_pci.c) | + |___________| |_________| |__________| |_____________________| + ^ ^ ^ ^ + |__________ | | _________| + | | | | pci_register_driver() + ___________________ pci_bus_*() __V___V_____________V__________V______ + | | pci_scan_root_bus() | | + | PCI BIOS |-------------------->| PCI Core | + | (arch/arm/kernel/ |<--------------------| (drivers/pci/pci* | + ----->| bios32.c)) |<--- pcibios_*() | drivers/pci/bus.c) | + | |___________________| | |______________________________________| + | ^ | + | | | pci_common_init_dev() + | | | + ____V___ ____V___ ___V____ + | | | | | | + | Renesas| | Tegra | | Exynos | + | PCI HC | | PCIe HC| | PCIe HC| drivers/pci/host/ + | driver | | driver | | driver | All these are + |________| |________| |________| PCI Root Complex drivers + | | | + | | | + V V V + platform_driver_register() + +Note: +Linux PCI subsystem is like above one without having a PCIe port bus stack. +For more details about this block see http://jagannadhteki.blog.com/2013/12/04/linux-pcie-subsystem/ + +PCI HC/RC driver +- Low level initialization and configuration (board, SoC) +- Invokes PCI-BIOS - for bus enumerations so that the endpoints on bus are ready. +- Supplies struct pci_ops to read/write config space. +- Setup the resources like bus numbers, memory/IO space, Interrupt numbers, MSI. +- Register PCI-BIOS as pci_common_init_dev() + +PCI BIOS +- Architecture specific PCI +- Bus enumeration - Lane, Bus, Device, Memory, Interrupt. +- Successful completion of BIOS assures that all the endpoints in bus are + assigned parts of available PCI resources and their respective Endpoint drivers + can take control of them using the functionalities provided by PCI Core. +- Register to PCI core for common accessing of endpoint drivers. +- pci_scan_root_bus() and pci_bus_*() + +PCI Core +- Provides services to Lower level BIOS and Upper level endpoint layers. +- Creates device entries for proc/sysfs information. +- Linux kernel PCI bus and driver management code. +- Provides set of abstraction functions that endpoint drivers can use to + initiate PCI communication with attached endpoints. +- Calls BIOS codes with pcibios_* + +PCI Endpoint driver +- Individual endpoint drivers from upper layer. +- Accessing config space upon respective endpoint enumeration done. +- Communicate over the endpoint for Tx/Rx transactions. +- Register to PCI core as pci_driver_register() + +PCIe Port Bus driver +- A logical PCI-PCI Bridge structure. +- Root Port and the Switch Port. +- See Documentation/PCI/pcie-portbus-howto.txt + +4. PCI HC/RC driver + +4.1 Description + +4.2 Sample code + +5. References +http://www.mindshare.com/files/ebooks/pci%20express%20system%20architecture.pdf +http://www.pcisig.com/developers/main/training_materials/ -- 1.8.3 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
