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Based on kernel version 4.9. Page generated on 2016-12-21 14:36 EST.

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*.
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