Add basic introductory documentation for the MEN Chameleon Bus.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxx>
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Documentation/MCB.txt | 162 ++++++++++++++++++++++++++++++++++++++++++++++++++
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+ MEN Chameleon Bus
+ =================
+
+Table of Contents
+=================
+1 Introduction
+ 1.1 Scope of this Document
+ 1.2 Limitations of the current implementation
+2 Architecture
+ 2.1 MEN Chameleon Bus
+ 2.2 Carrier Devices
+ 2.3 Parser
+3 Resource handling
+ 3.1 Memory Resources
+ 3.2 IRQs
+4 Writing a MCB driver
+ 4.1 The driver structure
+ 4.2 Probing and attaching
+ 4.3 Initializing the driver
+
+
+1 Introduction
+===============
+ This document describes the architecture and implementation of the MEN
+ Chameleon Bus (called MCB throughout this document).
+
+1.1 Scope of this Document
+---------------------------
+ This document is intended to be a short overview of the current
+ implementation and does by no means describe to complete possibilities of MCB
+ based devices.
+
+1.2 Limitations of the current implementation
+----------------------------------------------
+ The current implementation is limited to PCI and PCIe based carrier devices
+ that only use a single memory resource and share the PCI legacy IRQ. Not
+ implemented are:
+ - Multi-resource MCB devices like the VME Controller or M-Module carrier.
+ - MCB devices that need another MCB device, like SRAM for a DMA Controller's
+ buffer descriptors or a video controller's video memory.
+ - A per-carrier IRQ domain for carrier devices that have one (or more) IRQs
+ per MCB device like PCIe based carriers with MSI or MSI-X support.
+
+2 Architecture
+===============
+ MCB is divided in 3 functional blocks:
+ - The MEN Chameleon Bus itself,
+ - drivers for MCB Carrier Devices and
+ - the parser for the Chameleon table.
+
+2.1 MEN Chameleon Bus
+----------------------
+ The MEN Chameleon Bus is an artificial bus system that attaches to an MEN
+ Chameleon FPGA device. These devices are multi-function devices implemented
+ in a single FPGA and usually attached via some sort of PCI or PCIe link. Each
+ FPGA contains a header section describing the content of the FPGA. The header
+ lists the device id, PCI BAR, offset from the beginning of the PCI BAR, size
+ in the FPGA, interrupt number and some other properties currently not handled
+ by the MCB implementation.
+
+2.2 Carrier Devices
+--------------------
+ A carrier device is just an abstraction for the real world physical bus the
+ chameleon FPGA is attached to. Some IP Core drivers may need to interact with
+ properties of the carrier device (like querying the IRQ number of a PCI
+ device). To provide abstraction from the real hardware bus, an MCB carrier
+ device provides callback methods to translate the driver's MCB function calls
+ to hardware related function calls. For example a carrier device may
+ implement the get_irq() method which can be translate into a hardware bus
+ query for the IRQ number the device should use.
+
+2.3 Parser
+-----------
+ The parser reads the 1st 512 bytes of a chameleon device and parses the
+ chameleon table. Currently the parser only supports the Chameleon v2 variant
+ of the chameleon table but can easily be adopted to support an older or
+ possible future variant. While parsing the table's entries new MCB devices
+ are allocated and their resources are assigned according to the resource
+ assignment in the chameleon table. After resource assignment is finished, the
+ MCB devices are registered at the MCB and thus at the driver core of the
+ Linux kernel.
+
+3 Resource handling
+====================
+ The current implementation assigns exactly one memory and one IRQ resource
+ per MCB device. But this is likely going to change in the future.
+
+3.1 Memory Resources
+---------------------
+ Each MCB device has exactly one memory resource, which can be requested from
+ the MCB bus. This memory resource is the physical address of the MCB device
+ inside the carrier and is intended to be passed to ioremap() and friends. It
+ is already requested from the kernel by calling request_mem_region().
+
+3.2 IRQs
+---------
+ Each MCB device has exactly one IRQ resource, which can be requested from the
+ MCB bus. If a carrier device driver implements the ->get_irq() callback
+ method, the IRQ number assigned by the carrier device will be returned,
+ otherwise the IRQ number inside the chameleon table will be returned. This
+ number is suitable to be passed to request_irq().
+
+4 Writing a MCB driver
+=======================
+
+4.1 The driver structure
+-------------------------
+ Each MCB driver has a structure to identify the device driver as well as
+ device ids which identify the IP Core inside the FPGA. The driver structure
+ also contaings callback methods which get executed on driver probe and
+ removal from the system.
+
+
+ static const struct mcb_device_id foo_ids[] = {
+ { .device = 0x123 },
+ { }
+ };
+ MODULE_DEVICE_TABLE(mcb, foo_ids);
+
+ static struct mcb_driver foo_driver = {
+ driver = {
+ .name = "foo-bar",
+ .owner = THIS_MODULE,
+ },
+ .probe = foo_probe,
+ .remove = foo_remove,
+ .id_table = foo_ids,
+ };
+
+4.2 Probing and attaching
+--------------------------
+ When a driver is loaded and the MCB devices it services are found, the MCB
+ core will call the driver's probe callback method. When the driver is removed
+ from the system, the MCB core will call the driver's remove callback method.
+
+
+ static init foo_probe(struct mcb_device *mdev, const struct mcb_device_id *id);
+ static void foo_remove(struct mcb_device *mdev);
+
+4.3 Initializing the driver
+----------------------------
+ When the kernel is booted or your foo driver module is inserted, you have to
+ perform driver initialization. Usually it is enough to register your driver
+ module at the MCB core.
+
+
+ static int __init foo_init(void)
+ {
+ return mcb_register_driver(&foo_driver);
+ }
+ module_init(foo_init);
+
+ static void __exit foo_exit(void)
+ {
+ mcb_unregister_driver(&foo_driver);
+ }
+ module_exit(foo_exit);
+
+ The module_mcb_driver() macro can be used to reduce the above code.
+
+
+ module_mcb_driver(foo_driver);
--
1.9.1
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