1================= 2MEN Chameleon Bus 3================= 4 5.. Table of Contents 6 ================= 7 1 Introduction 8 1.1 Scope of this Document 9 1.2 Limitations of the current implementation 10 2 Architecture 11 2.1 MEN Chameleon Bus 12 2.2 Carrier Devices 13 2.3 Parser 14 3 Resource handling 15 3.1 Memory Resources 16 3.2 IRQs 17 4 Writing an MCB driver 18 4.1 The driver structure 19 4.2 Probing and attaching 20 4.3 Initializing the driver 21 22 23Introduction 24============ 25 26This document describes the architecture and implementation of the MEN 27Chameleon Bus (called MCB throughout this document). 28 29Scope of this Document 30---------------------- 31 32This document is intended to be a short overview of the current 33implementation and does by no means describe the complete possibilities of MCB 34based devices. 35 36Limitations of the current implementation 37----------------------------------------- 38 39The current implementation is limited to PCI and PCIe based carrier devices 40that only use a single memory resource and share the PCI legacy IRQ. Not 41implemented are: 42 43- Multi-resource MCB devices like the VME Controller or M-Module carrier. 44- MCB devices that need another MCB device, like SRAM for a DMA Controller's 45 buffer descriptors or a video controller's video memory. 46- A per-carrier IRQ domain for carrier devices that have one (or more) IRQs 47 per MCB device like PCIe based carriers with MSI or MSI-X support. 48 49Architecture 50============ 51 52MCB is divided into 3 functional blocks: 53 54- The MEN Chameleon Bus itself, 55- drivers for MCB Carrier Devices and 56- the parser for the Chameleon table. 57 58MEN Chameleon Bus 59----------------- 60 61The MEN Chameleon Bus is an artificial bus system that attaches to a so 62called Chameleon FPGA device found on some hardware produced my MEN Mikro 63Elektronik GmbH. These devices are multi-function devices implemented in a 64single FPGA and usually attached via some sort of PCI or PCIe link. Each 65FPGA contains a header section describing the content of the FPGA. The 66header lists the device id, PCI BAR, offset from the beginning of the PCI 67BAR, size in the FPGA, interrupt number and some other properties currently 68not handled by the MCB implementation. 69 70Carrier Devices 71--------------- 72 73A carrier device is just an abstraction for the real world physical bus the 74Chameleon FPGA is attached to. Some IP Core drivers may need to interact with 75properties of the carrier device (like querying the IRQ number of a PCI 76device). To provide abstraction from the real hardware bus, an MCB carrier 77device provides callback methods to translate the driver's MCB function calls 78to hardware related function calls. For example a carrier device may 79implement the get_irq() method which can be translated into a hardware bus 80query for the IRQ number the device should use. 81 82Parser 83------ 84 85The parser reads the first 512 bytes of a Chameleon device and parses the 86Chameleon table. Currently the parser only supports the Chameleon v2 variant 87of the Chameleon table but can easily be adopted to support an older or 88possible future variant. While parsing the table's entries new MCB devices 89are allocated and their resources are assigned according to the resource 90assignment in the Chameleon table. After resource assignment is finished, the 91MCB devices are registered at the MCB and thus at the driver core of the 92Linux kernel. 93 94Resource handling 95================= 96 97The current implementation assigns exactly one memory and one IRQ resource 98per MCB device. But this is likely going to change in the future. 99 100Memory Resources 101---------------- 102 103Each MCB device has exactly one memory resource, which can be requested from 104the MCB bus. This memory resource is the physical address of the MCB device 105inside the carrier and is intended to be passed to ioremap() and friends. It 106is already requested from the kernel by calling request_mem_region(). 107 108IRQs 109---- 110 111Each MCB device has exactly one IRQ resource, which can be requested from the 112MCB bus. If a carrier device driver implements the ->get_irq() callback 113method, the IRQ number assigned by the carrier device will be returned, 114otherwise the IRQ number inside the Chameleon table will be returned. This 115number is suitable to be passed to request_irq(). 116 117Writing an MCB driver 118===================== 119 120The driver structure 121-------------------- 122 123Each MCB driver has a structure to identify the device driver as well as 124device ids which identify the IP Core inside the FPGA. The driver structure 125also contains callback methods which get executed on driver probe and 126removal from the system:: 127 128 static const struct mcb_device_id foo_ids[] = { 129 { .device = 0x123 }, 130 { } 131 }; 132 MODULE_DEVICE_TABLE(mcb, foo_ids); 133 134 static struct mcb_driver foo_driver = { 135 driver = { 136 .name = "foo-bar", 137 .owner = THIS_MODULE, 138 }, 139 .probe = foo_probe, 140 .remove = foo_remove, 141 .id_table = foo_ids, 142 }; 143 144Probing and attaching 145--------------------- 146 147When a driver is loaded and the MCB devices it services are found, the MCB 148core will call the driver's probe callback method. When the driver is removed 149from the system, the MCB core will call the driver's remove callback method:: 150 151 static init foo_probe(struct mcb_device *mdev, const struct mcb_device_id *id); 152 static void foo_remove(struct mcb_device *mdev); 153 154Initializing the driver 155----------------------- 156 157When the kernel is booted or your foo driver module is inserted, you have to 158perform driver initialization. Usually it is enough to register your driver 159module at the MCB core:: 160 161 static int __init foo_init(void) 162 { 163 return mcb_register_driver(&foo_driver); 164 } 165 module_init(foo_init); 166 167 static void __exit foo_exit(void) 168 { 169 mcb_unregister_driver(&foo_driver); 170 } 171 module_exit(foo_exit); 172 173The module_mcb_driver() macro can be used to reduce the above code:: 174 175 module_mcb_driver(foo_driver); 176