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1 | # NTB Drivers |
2 | |
3 | NTB (Non-Transparent Bridge) is a type of PCI-Express bridge chip that connects |
4 | the separate memory systems of two computers to the same PCI-Express fabric. |
5 | Existing NTB hardware supports a common feature set, including scratchpad |
6 | registers, doorbell registers, and memory translation windows. Scratchpad |
7 | registers are read-and-writable registers that are accessible from either side |
8 | of the device, so that peers can exchange a small amount of information at a |
9 | fixed address. Doorbell registers provide a way for peers to send interrupt |
10 | events. Memory windows allow translated read and write access to the peer |
11 | memory. |
12 | |
13 | ## NTB Core Driver (ntb) |
14 | |
15 | The NTB core driver defines an api wrapping the common feature set, and allows |
16 | clients interested in NTB features to discover NTB the devices supported by |
17 | hardware drivers. The term "client" is used here to mean an upper layer |
18 | component making use of the NTB api. The term "driver," or "hardware driver," |
19 | is used here to mean a driver for a specific vendor and model of NTB hardware. |
20 | |
21 | ## NTB Client Drivers |
22 | |
23 | NTB client drivers should register with the NTB core driver. After |
24 | registering, the client probe and remove functions will be called appropriately |
25 | as ntb hardware, or hardware drivers, are inserted and removed. The |
26 | registration uses the Linux Device framework, so it should feel familiar to |
27 | anyone who has written a pci driver. |
28 | |
29 | ### NTB Transport Client (ntb\_transport) and NTB Netdev (ntb\_netdev) |
30 | |
31 | The primary client for NTB is the Transport client, used in tandem with NTB |
32 | Netdev. These drivers function together to create a logical link to the peer, |
33 | across the ntb, to exchange packets of network data. The Transport client |
34 | establishes a logical link to the peer, and creates queue pairs to exchange |
35 | messages and data. The NTB Netdev then creates an ethernet device using a |
36 | Transport queue pair. Network data is copied between socket buffers and the |
37 | Transport queue pair buffer. The Transport client may be used for other things |
38 | besides Netdev, however no other applications have yet been written. |
39 | |
40 | ### NTB Ping Pong Test Client (ntb\_pingpong) |
41 | |
42 | The Ping Pong test client serves as a demonstration to exercise the doorbell |
43 | and scratchpad registers of NTB hardware, and as an example simple NTB client. |
44 | Ping Pong enables the link when started, waits for the NTB link to come up, and |
45 | then proceeds to read and write the doorbell scratchpad registers of the NTB. |
46 | The peers interrupt each other using a bit mask of doorbell bits, which is |
47 | shifted by one in each round, to test the behavior of multiple doorbell bits |
48 | and interrupt vectors. The Ping Pong driver also reads the first local |
49 | scratchpad, and writes the value plus one to the first peer scratchpad, each |
50 | round before writing the peer doorbell register. |
51 | |
52 | Module Parameters: |
53 | |
54 | * unsafe - Some hardware has known issues with scratchpad and doorbell |
55 | registers. By default, Ping Pong will not attempt to exercise such |
56 | hardware. You may override this behavior at your own risk by setting |
57 | unsafe=1. |
58 | * delay\_ms - Specify the delay between receiving a doorbell |
59 | interrupt event and setting the peer doorbell register for the next |
60 | round. |
61 | * init\_db - Specify the doorbell bits to start new series of rounds. A new |
62 | series begins once all the doorbell bits have been shifted out of |
63 | range. |
64 | * dyndbg - It is suggested to specify dyndbg=+p when loading this module, and |
65 | then to observe debugging output on the console. |
66 | |
67 | ### NTB Tool Test Client (ntb\_tool) |
68 | |
69 | The Tool test client serves for debugging, primarily, ntb hardware and drivers. |
70 | The Tool provides access through debugfs for reading, setting, and clearing the |
71 | NTB doorbell, and reading and writing scratchpads. |
72 | |
73 | The Tool does not currently have any module parameters. |
74 | |
75 | Debugfs Files: |
76 | |
77 | * *debugfs*/ntb\_tool/*hw*/ - A directory in debugfs will be created for each |
78 | NTB device probed by the tool. This directory is shortened to *hw* |
79 | below. |
80 | * *hw*/db - This file is used to read, set, and clear the local doorbell. Not |
81 | all operations may be supported by all hardware. To read the doorbell, |
82 | read the file. To set the doorbell, write `s` followed by the bits to |
83 | set (eg: `echo 's 0x0101' > db`). To clear the doorbell, write `c` |
84 | followed by the bits to clear. |
85 | * *hw*/mask - This file is used to read, set, and clear the local doorbell mask. |
86 | See *db* for details. |
87 | * *hw*/peer\_db - This file is used to read, set, and clear the peer doorbell. |
88 | See *db* for details. |
89 | * *hw*/peer\_mask - This file is used to read, set, and clear the peer doorbell |
90 | mask. See *db* for details. |
91 | * *hw*/spad - This file is used to read and write local scratchpads. To read |
92 | the values of all scratchpads, read the file. To write values, write a |
93 | series of pairs of scratchpad number and value |
94 | (eg: `echo '4 0x123 7 0xabc' > spad` |
95 | # to set scratchpads `4` and `7` to `0x123` and `0xabc`, respectively). |
96 | * *hw*/peer\_spad - This file is used to read and write peer scratchpads. See |
97 | *spad* for details. |
98 | |
99 | ## NTB Hardware Drivers |
100 | |
101 | NTB hardware drivers should register devices with the NTB core driver. After |
102 | registering, clients probe and remove functions will be called. |
103 | |
104 | ### NTB Intel Hardware Driver (ntb\_hw\_intel) |
105 | |
106 | The Intel hardware driver supports NTB on Xeon and Atom CPUs. |
107 | |
108 | Module Parameters: |
109 | |
110 | * b2b\_mw\_idx - If the peer ntb is to be accessed via a memory window, then use |
111 | this memory window to access the peer ntb. A value of zero or positive |
112 | starts from the first mw idx, and a negative value starts from the last |
113 | mw idx. Both sides MUST set the same value here! The default value is |
114 | `-1`. |
115 | * b2b\_mw\_share - If the peer ntb is to be accessed via a memory window, and if |
116 | the memory window is large enough, still allow the client to use the |
117 | second half of the memory window for address translation to the peer. |
118 | * xeon\_b2b\_usd\_bar2\_addr64 - If using B2B topology on Xeon hardware, use |
119 | this 64 bit address on the bus between the NTB devices for the window |
120 | at BAR2, on the upstream side of the link. |
121 | * xeon\_b2b\_usd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*. |
122 | * xeon\_b2b\_usd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*. |
123 | * xeon\_b2b\_usd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*. |
124 | * xeon\_b2b\_dsd\_bar2\_addr64 - See *xeon\_b2b\_bar2\_addr64*. |
125 | * xeon\_b2b\_dsd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*. |
126 | * xeon\_b2b\_dsd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*. |
127 | * xeon\_b2b\_dsd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*. |
128 |