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  1 # NTB Drivers
  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.
 13 ## NTB Core Driver (ntb)
 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.
 21 ## NTB Client Drivers
 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.
 29 ### NTB Transport Client (ntb\_transport) and NTB Netdev (ntb\_netdev)
 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.
 40 ### NTB Ping Pong Test Client (ntb\_pingpong)
 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.
 52 Module Parameters:
 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.
 67 ### NTB Tool Test Client (ntb\_tool)
 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.
 73 The Tool does not currently have any module parameters.
 75 Debugfs Files:
 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.
 99 ## NTB Hardware Drivers
101 NTB hardware drivers should register devices with the NTB core driver.  After
102 registering, clients probe and remove functions will be called.
104 ### NTB Intel Hardware Driver (ntb\_hw\_intel)
106 The Intel hardware driver supports NTB on Xeon and Atom CPUs.
108 Module Parameters:
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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