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Date: Wed, 11 Dec 2013 09:32:58 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Jagannadha Sutradharudu Teki
<jagannadha.sutradharudu-teki@...inx.com>,
Bjorn Helgaas <bhelgaas@...gle.com>
CC: Rob Landley <rob@...dley.net>, linux-pci@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
Jagannadha Sutradharudu Teki <jaganna@...inx.com>
Subject: Re: [PATCH 2/2] Documentation: pci: Add pcie-howto.txt
On 12/11/13 01:15, Jagannadha Sutradharudu Teki wrote:
> Added pcie-howto.txt for describing the information
> on PCI Express basics and Root Complex driver.
>
> Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@...inx.com>
> ---
> Documentation/PCI/00-INDEX | 2 +
> Documentation/PCI/pcie-howto.txt | 184 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 186 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..963cb75
> --- /dev/null
> +++ b/Documentation/PCI/pcie-howto.txt
> @@ -0,0 +1,184 @@
> + PCI Express HOWTO
> + Jagannadha Sutradharudu Teki <jagannadh.teki@...il.com>
> + 05/12/2013
> +
> +1. About this guide
> +
> +This guide describes the basics of the PCI Express and provides
Express bus and
> +information on how Linux PCIe subsystem looks like and at last
what the Linux and ends
> +with brief description of PCI Host controller/Root complex driver
with a brief
> +along with some sample code.
> +
> +2. Basic terminology and conventions
> +
> +PCI Express is
> +- A high performance, IO interconnect for peripherals.
^drop comma
> +- 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.
packet-based
> +- 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
These
> +referred to as Lanes.
> +
> +Upstream Port
> +Port that points in the direction of RC.
> +
> +Downstream Port
> +Port the points away from the RC.
that
> +
> +Root Port
> +Whose upstream port is RC and dowstream port should be a EP or Bridge.
an
> +
> +Switch Port
> +Whose upstream port is RC and dowstream port is always be a switch.
always a switch.
> +
> +Endpoint (EP)
> +Devices other than RC, Switches and Bridges which either generates or terminates a PCIe
generate or terminate
> +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| | Tergra | | Exynos |
Tegra
> + | 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 have a PCIe port bus stack.
having
> +For more details abou this block see http://jagannadhteki.blog.com/2013/12/04/linux-pcie-subsystem/
about
> +
> +PCI HC/RC driver
> +- Low level initialization and configuration (board, soc)
SOC or SoC, please
> +- Invokes PCI-BIOS - for bus enumerations so-that the endpoints on bus is ready.
so that are
> +- 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.
> +- Enumeration ends up with scanning all endpoints on bus got discovered.
^^^ confusing
> +- 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.
PCI
> +- Provides set of abstraction functions that endpoint drivers can used to
use
> + initiate pci communication with attached endpoints.
PCI
> +- 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-busport-howto.txt
~~~~~~~
portbus
--
~Randy
--
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