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*.