1 =================
2 MEN 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 4.4 Using DMA
22
23
24 Introduction
25 ============
26
27 This document describes the architecture and implementation of the MEN
28 Chameleon Bus (called MCB throughout this document).
29
30 Scope of this Document
31 ----------------------
32
33 This document is intended to be a short overview of the current
34 implementation and does by no means describe the complete possibilities of MCB
35 based devices.
36
37 Limitations of the current implementation
38 -----------------------------------------
39
40 The current implementation is limited to PCI and PCIe based carrier devices
41 that only use a single memory resource and share the PCI legacy IRQ. Not
42 implemented are:
43
44 - Multi-resource MCB devices like the VME Controller or M-Module carrier.
45 - MCB devices that need another MCB device, like SRAM for a DMA Controller's
46 buffer descriptors or a video controller's video memory.
47 - A per-carrier IRQ domain for carrier devices that have one (or more) IRQs
48 per MCB device like PCIe based carriers with MSI or MSI-X support.
49
50 Architecture
51 ============
52
53 MCB is divided into 3 functional blocks:
54
55 - The MEN Chameleon Bus itself,
56 - drivers for MCB Carrier Devices and
57 - the parser for the Chameleon table.
58
59 MEN Chameleon Bus
60 -----------------
61
62 The MEN Chameleon Bus is an artificial bus system that attaches to a so
63 called Chameleon FPGA device found on some hardware produced my MEN Mikro
64 Elektronik GmbH. These devices are multi-function devices implemented in a
65 single FPGA and usually attached via some sort of PCI or PCIe link. Each
66 FPGA contains a header section describing the content of the FPGA. The
67 header lists the device id, PCI BAR, offset from the beginning of the PCI
68 BAR, size in the FPGA, interrupt number and some other properties currently
69 not handled by the MCB implementation.
70
71 Carrier Devices
72 ---------------
73
74 A carrier device is just an abstraction for the real world physical bus the
75 Chameleon FPGA is attached to. Some IP Core drivers may need to interact with
76 properties of the carrier device (like querying the IRQ number of a PCI
77 device). To provide abstraction from the real hardware bus, an MCB carrier
78 device provides callback methods to translate the driver's MCB function calls
79 to hardware related function calls. For example a carrier device may
80 implement the get_irq() method which can be translated into a hardware bus
81 query for the IRQ number the device should use.
82
83 Parser
84 ------
85
86 The parser reads the first 512 bytes of a Chameleon device and parses the
87 Chameleon table. Currently the parser only supports the Chameleon v2 variant
88 of the Chameleon table but can easily be adopted to support an older or
89 possible future variant. While parsing the table's entries new MCB devices
90 are allocated and their resources are assigned according to the resource
91 assignment in the Chameleon table. After resource assignment is finished, the
92 MCB devices are registered at the MCB and thus at the driver core of the
93 Linux kernel.
94
95 Resource handling
96 =================
97
98 The current implementation assigns exactly one memory and one IRQ resource
99 per MCB device. But this is likely going to change in the future.
100
101 Memory Resources
102 ----------------
103
104 Each MCB device has exactly one memory resource, which can be requested from
105 the MCB bus. This memory resource is the physical address of the MCB device
106 inside the carrier and is intended to be passed to ioremap() and friends. It
107 is already requested from the kernel by calling request_mem_region().
108
109 IRQs
110 ----
111
112 Each MCB device has exactly one IRQ resource, which can be requested from the
113 MCB bus. If a carrier device driver implements the ->get_irq() callback
114 method, the IRQ number assigned by the carrier device will be returned,
115 otherwise the IRQ number inside the Chameleon table will be returned. This
116 number is suitable to be passed to request_irq().
117
118 Writing an MCB driver
119 =====================
120
121 The driver structure
122 --------------------
123
124 Each MCB driver has a structure to identify the device driver as well as
125 device ids which identify the IP Core inside the FPGA. The driver structure
126 also contains callback methods which get executed on driver probe and
127 removal from the system::
128
129 static const struct mcb_device_id foo_ids[] = {
130 { .device = 0x123 },
131 { }
132 };
133 MODULE_DEVICE_TABLE(mcb, foo_ids);
134
135 static struct mcb_driver foo_driver = {
136 driver = {
137 .name = "foo-bar",
138 .owner = THIS_MODULE,
139 },
140 .probe = foo_probe,
141 .remove = foo_remove,
142 .id_table = foo_ids,
143 };
144
145 Probing and attaching
146 ---------------------
147
148 When a driver is loaded and the MCB devices it services are found, the MCB
149 core will call the driver's probe callback method. When the driver is removed
150 from the system, the MCB core will call the driver's remove callback method::
151
152 static init foo_probe(struct mcb_device *mdev, const struct mcb_device_id *id);
153 static void foo_remove(struct mcb_device *mdev);
154
155 Initializing the driver
156 -----------------------
157
158 When the kernel is booted or your foo driver module is inserted, you have to
159 perform driver initialization. Usually it is enough to register your driver
160 module at the MCB core::
161
162 static int __init foo_init(void)
163 {
164 return mcb_register_driver(&foo_driver);
165 }
166 module_init(foo_init);
167
168 static void __exit foo_exit(void)
169 {
170 mcb_unregister_driver(&foo_driver);
171 }
172 module_exit(foo_exit);
173
174 The module_mcb_driver() macro can be used to reduce the above code::
175
176 module_mcb_driver(foo_driver);
177
178 Using DMA
179 ---------
180
181 To make use of the kernel's DMA-API's function, you will need to use the
182 carrier device's 'struct device'. Fortunately 'struct mcb_device' embeds a
183 pointer (->dma_dev) to the carrier's device for DMA purposes::
184
185 ret = dma_set_mask_and_coherent(&mdev->dma_dev, DMA_BIT_MASK(dma_bits));
186 if (rc)
187 /* Handle errors */
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