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0001 # NTB Drivers
0002 
0003 NTB (Non-Transparent Bridge) is a type of PCI-Express bridge chip that connects
0004 the separate memory systems of two computers to the same PCI-Express fabric.
0005 Existing NTB hardware supports a common feature set, including scratchpad
0006 registers, doorbell registers, and memory translation windows.  Scratchpad
0007 registers are read-and-writable registers that are accessible from either side
0008 of the device, so that peers can exchange a small amount of information at a
0009 fixed address.  Doorbell registers provide a way for peers to send interrupt
0010 events.  Memory windows allow translated read and write access to the peer
0011 memory.
0012 
0013 ## NTB Core Driver (ntb)
0014 
0015 The NTB core driver defines an api wrapping the common feature set, and allows
0016 clients interested in NTB features to discover NTB the devices supported by
0017 hardware drivers.  The term "client" is used here to mean an upper layer
0018 component making use of the NTB api.  The term "driver," or "hardware driver,"
0019 is used here to mean a driver for a specific vendor and model of NTB hardware.
0020 
0021 ## NTB Client Drivers
0022 
0023 NTB client drivers should register with the NTB core driver.  After
0024 registering, the client probe and remove functions will be called appropriately
0025 as ntb hardware, or hardware drivers, are inserted and removed.  The
0026 registration uses the Linux Device framework, so it should feel familiar to
0027 anyone who has written a pci driver.
0028 
0029 ### NTB Transport Client (ntb\_transport) and NTB Netdev (ntb\_netdev)
0030 
0031 The primary client for NTB is the Transport client, used in tandem with NTB
0032 Netdev.  These drivers function together to create a logical link to the peer,
0033 across the ntb, to exchange packets of network data.  The Transport client
0034 establishes a logical link to the peer, and creates queue pairs to exchange
0035 messages and data.  The NTB Netdev then creates an ethernet device using a
0036 Transport queue pair.  Network data is copied between socket buffers and the
0037 Transport queue pair buffer.  The Transport client may be used for other things
0038 besides Netdev, however no other applications have yet been written.
0039 
0040 ### NTB Ping Pong Test Client (ntb\_pingpong)
0041 
0042 The Ping Pong test client serves as a demonstration to exercise the doorbell
0043 and scratchpad registers of NTB hardware, and as an example simple NTB client.
0044 Ping Pong enables the link when started, waits for the NTB link to come up, and
0045 then proceeds to read and write the doorbell scratchpad registers of the NTB.
0046 The peers interrupt each other using a bit mask of doorbell bits, which is
0047 shifted by one in each round, to test the behavior of multiple doorbell bits
0048 and interrupt vectors.  The Ping Pong driver also reads the first local
0049 scratchpad, and writes the value plus one to the first peer scratchpad, each
0050 round before writing the peer doorbell register.
0051 
0052 Module Parameters:
0053 
0054 * unsafe - Some hardware has known issues with scratchpad and doorbell
0055         registers.  By default, Ping Pong will not attempt to exercise such
0056         hardware.  You may override this behavior at your own risk by setting
0057         unsafe=1.
0058 * delay\_ms - Specify the delay between receiving a doorbell
0059         interrupt event and setting the peer doorbell register for the next
0060         round.
0061 * init\_db - Specify the doorbell bits to start new series of rounds.  A new
0062         series begins once all the doorbell bits have been shifted out of
0063         range.
0064 * dyndbg - It is suggested to specify dyndbg=+p when loading this module, and
0065         then to observe debugging output on the console.
0066 
0067 ### NTB Tool Test Client (ntb\_tool)
0068 
0069 The Tool test client serves for debugging, primarily, ntb hardware and drivers.
0070 The Tool provides access through debugfs for reading, setting, and clearing the
0071 NTB doorbell, and reading and writing scratchpads.
0072 
0073 The Tool does not currently have any module parameters.
0074 
0075 Debugfs Files:
0076 
0077 * *debugfs*/ntb\_tool/*hw*/ - A directory in debugfs will be created for each
0078         NTB device probed by the tool.  This directory is shortened to *hw*
0079         below.
0080 * *hw*/db - This file is used to read, set, and clear the local doorbell.  Not
0081         all operations may be supported by all hardware.  To read the doorbell,
0082         read the file.  To set the doorbell, write `s` followed by the bits to
0083         set (eg: `echo 's 0x0101' > db`).  To clear the doorbell, write `c`
0084         followed by the bits to clear.
0085 * *hw*/mask - This file is used to read, set, and clear the local doorbell mask.
0086         See *db* for details.
0087 * *hw*/peer\_db - This file is used to read, set, and clear the peer doorbell.
0088         See *db* for details.
0089 * *hw*/peer\_mask - This file is used to read, set, and clear the peer doorbell
0090         mask.  See *db* for details.
0091 * *hw*/spad - This file is used to read and write local scratchpads.  To read
0092         the values of all scratchpads, read the file.  To write values, write a
0093         series of pairs of scratchpad number and value
0094         (eg: `echo '4 0x123 7 0xabc' > spad`
0095         # to set scratchpads `4` and `7` to `0x123` and `0xabc`, respectively).
0096 * *hw*/peer\_spad - This file is used to read and write peer scratchpads.  See
0097         *spad* for details.
0098 
0099 ## NTB Hardware Drivers
0100 
0101 NTB hardware drivers should register devices with the NTB core driver.  After
0102 registering, clients probe and remove functions will be called.
0103 
0104 ### NTB Intel Hardware Driver (ntb\_hw\_intel)
0105 
0106 The Intel hardware driver supports NTB on Xeon and Atom CPUs.
0107 
0108 Module Parameters:
0109 
0110 * b2b\_mw\_idx - If the peer ntb is to be accessed via a memory window, then use
0111         this memory window to access the peer ntb.  A value of zero or positive
0112         starts from the first mw idx, and a negative value starts from the last
0113         mw idx.  Both sides MUST set the same value here!  The default value is
0114         `-1`.
0115 * b2b\_mw\_share - If the peer ntb is to be accessed via a memory window, and if
0116         the memory window is large enough, still allow the client to use the
0117         second half of the memory window for address translation to the peer.
0118 * xeon\_b2b\_usd\_bar2\_addr64 - If using B2B topology on Xeon hardware, use
0119         this 64 bit address on the bus between the NTB devices for the window
0120         at BAR2, on the upstream side of the link.
0121 * xeon\_b2b\_usd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
0122 * xeon\_b2b\_usd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
0123 * xeon\_b2b\_usd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
0124 * xeon\_b2b\_dsd\_bar2\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
0125 * xeon\_b2b\_dsd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
0126 * xeon\_b2b\_dsd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
0127 * xeon\_b2b\_dsd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*.