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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-06-27 15:39:22 -0300 |
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committer | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-07-15 11:03:02 -0300 |
commit | baa293e9544bea71361950d071579f0e4d5713ed (patch) | |
tree | 29e0400c806016783a3fd7a380be40a201956653 /Documentation/driver-api/men-chameleon-bus.rst | |
parent | 4f4cfa6c560c93ba180c30675cf845e1597de44c (diff) | |
download | linux-baa293e9544bea71361950d071579f0e4d5713ed.tar.gz linux-baa293e9544bea71361950d071579f0e4d5713ed.tar.bz2 linux-baa293e9544bea71361950d071579f0e4d5713ed.zip |
docs: driver-api: add a series of orphaned documents
There are lots of documents under Documentation/*.txt and a few other
orphan documents elsehwere that belong to the driver-API book.
Move them to their right place.
Reviewed-by: Cornelia Huck <cohuck@redhat.com> # vfio-related parts
Acked-by: Logan Gunthorpe <logang@deltatee.com> # switchtec
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/driver-api/men-chameleon-bus.rst')
-rw-r--r-- | Documentation/driver-api/men-chameleon-bus.rst | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/Documentation/driver-api/men-chameleon-bus.rst b/Documentation/driver-api/men-chameleon-bus.rst new file mode 100644 index 000000000000..1b1f048aa748 --- /dev/null +++ b/Documentation/driver-api/men-chameleon-bus.rst @@ -0,0 +1,175 @@ +================= +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 an MCB driver + 4.1 The driver structure + 4.2 Probing and attaching + 4.3 Initializing the driver + + +Introduction +============ + +This document describes the architecture and implementation of the MEN +Chameleon Bus (called MCB throughout this document). + +Scope of this Document +---------------------- + +This document is intended to be a short overview of the current +implementation and does by no means describe the complete possibilities of MCB +based devices. + +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. + +Architecture +============ + +MCB is divided into 3 functional blocks: + +- The MEN Chameleon Bus itself, +- drivers for MCB Carrier Devices and +- the parser for the Chameleon table. + +MEN Chameleon Bus +----------------- + +The MEN Chameleon Bus is an artificial bus system that attaches to a so +called Chameleon FPGA device found on some hardware produced my MEN Mikro +Elektronik GmbH. 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. + +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 translated into a hardware bus +query for the IRQ number the device should use. + +Parser +------ + +The parser reads the first 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. + +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. + +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(). + +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(). + +Writing an MCB driver +===================== + +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 contains 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, + }; + +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); + +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); |