1# NTB Drivers
   3NTB (Non-Transparent Bridge) is a type of PCI-Express bridge chip that connects
   4the separate memory systems of two computers to the same PCI-Express fabric.
   5Existing NTB hardware supports a common feature set, including scratchpad
   6registers, doorbell registers, and memory translation windows.  Scratchpad
   7registers are read-and-writable registers that are accessible from either side
   8of the device, so that peers can exchange a small amount of information at a
   9fixed address.  Doorbell registers provide a way for peers to send interrupt
  10events.  Memory windows allow translated read and write access to the peer
  13## NTB Core Driver (ntb)
  15The NTB core driver defines an api wrapping the common feature set, and allows
  16clients interested in NTB features to discover NTB the devices supported by
  17hardware drivers.  The term "client" is used here to mean an upper layer
  18component making use of the NTB api.  The term "driver," or "hardware driver,"
  19is used here to mean a driver for a specific vendor and model of NTB hardware.
  21## NTB Client Drivers
  23NTB client drivers should register with the NTB core driver.  After
  24registering, the client probe and remove functions will be called appropriately
  25as ntb hardware, or hardware drivers, are inserted and removed.  The
  26registration uses the Linux Device framework, so it should feel familiar to
  27anyone who has written a pci driver.
  29### NTB Transport Client (ntb\_transport) and NTB Netdev (ntb\_netdev)
  31The primary client for NTB is the Transport client, used in tandem with NTB
  32Netdev.  These drivers function together to create a logical link to the peer,
  33across the ntb, to exchange packets of network data.  The Transport client
  34establishes a logical link to the peer, and creates queue pairs to exchange
  35messages and data.  The NTB Netdev then creates an ethernet device using a
  36Transport queue pair.  Network data is copied between socket buffers and the
  37Transport queue pair buffer.  The Transport client may be used for other things
  38besides Netdev, however no other applications have yet been written.
  40### NTB Ping Pong Test Client (ntb\_pingpong)
  42The Ping Pong test client serves as a demonstration to exercise the doorbell
  43and scratchpad registers of NTB hardware, and as an example simple NTB client.
  44Ping Pong enables the link when started, waits for the NTB link to come up, and
  45then proceeds to read and write the doorbell scratchpad registers of the NTB.
  46The peers interrupt each other using a bit mask of doorbell bits, which is
  47shifted by one in each round, to test the behavior of multiple doorbell bits
  48and interrupt vectors.  The Ping Pong driver also reads the first local
  49scratchpad, and writes the value plus one to the first peer scratchpad, each
  50round before writing the peer doorbell register.
  52Module 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)
  69The Tool test client serves for debugging, primarily, ntb hardware and drivers.
  70The Tool provides access through debugfs for reading, setting, and clearing the
  71NTB doorbell, and reading and writing scratchpads.
  73The Tool does not currently have any module parameters.
  75Debugfs 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
 101NTB hardware drivers should register devices with the NTB core driver.  After
 102registering, clients probe and remove functions will be called.
 104### NTB Intel Hardware Driver (ntb\_hw\_intel)
 106The Intel hardware driver supports NTB on Xeon and Atom CPUs.
 108Module 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*.