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without incorporating them into the Sphinx tree. The hope is to bring some uniformity to kernel documentation and, perhaps more importantly, have our existing docs serve as an example of the desired formatting for those that will be added later. -----BEGIN PGP SIGNATURE----- iQJDBAABCAAtFiEEUOvtSCFqLxY/7px3jc41VjAi5XoFAllpIuQPHGNvcmJldEBs d24ubmV0AAoJEI3ONVYwIuV66VIP/1GNACrp606m7HAvfskGyt26RB7hwM3+5ct2 4LDwBW8l1IZ5efgMFsEur9QjMPexiDCkzYqNj4B8vjQLk2dVl5w+eMJ4KY5hRGHe dfZtyTrbzh9gQtPOufNXkTiFJBQXlbrcoLb9JK0S8OdC9LM6yN5wNwTHddmoieiC +cmSt5iPf2/olNqZjtjAK/ZS+AHMb3C+Um/tMamiV5uMXmCWA9Xsz1HWZKbB3WVe X7zLiyt5BVAOLXKir8fCUNMh0qTkq4K+mDVC7TPnHae+fAudjA+sZycuJr2ebNtR JK15wWArUaQj7G90eB8VM1ZCN8eyYaUxXpHGw5+2A5p7gXvytfiF2VahJfJLLSjK gM7ZZcwynYe7/tzqf2Bmz7uqnAqm9cSMdxplGPdoqq0RUCE+nFDoslbcGw+0YS+c OM8FxCMNHYdjtX18pKQZ4H2KJ2qy5FqA0tyRnlWDj6+pNPQeAQoQ2zUEq0w/qSk6 ArQAxaNhuhPjhaqL8qhyd3MnTAncWAIbuW6FBd5RbyYmGz/jJ0srxRwnrJEZzFc9 LaDUSDPZ8frtLd8nVNHgblD2yBWAwRMcFbwt5oZS2yIYPg6VBdHyCosZBDTsmZP0 7IIeW5trsagK2ktp2KooPZ5cOgeXzLmUnEDPEoMoJ6yPSsHvDDzpItJLot8HZrH2 ahaOgM3e =HvQS -----END PGP SIGNATURE----- Merge tag 'standardize-docs' of git://git.lwn.net/linux Pull documentation format standardization from Jonathan Corbet: "This series converts a number of top-level documents to the RST format without incorporating them into the Sphinx tree. The hope is to bring some uniformity to kernel documentation and, perhaps more importantly, have our existing docs serve as an example of the desired formatting for those that will be added later. Mauro has gone through and fixed up a lot of top-level documentation files to make them conform to the RST format, but without moving or renaming them in any way. This will help when we incorporate the ones we want to keep into the Sphinx doctree, but the real purpose is to bring a bit of uniformity to our documentation and let the top-level docs serve as examples for those writing new ones" * tag 'standardize-docs' of git://git.lwn.net/linux: (84 commits) docs: kprobes.txt: Fix whitespacing tee.txt: standardize document format cgroup-v2.txt: standardize document format dell_rbu.txt: standardize document format zorro.txt: standardize document format xz.txt: standardize document format xillybus.txt: standardize document format vfio.txt: standardize document format vfio-mediated-device.txt: standardize document format unaligned-memory-access.txt: standardize document format this_cpu_ops.txt: standardize document format svga.txt: standardize document format static-keys.txt: standardize document format smsc_ece1099.txt: standardize document format SM501.txt: standardize document format siphash.txt: standardize document format sgi-ioc4.txt: standardize document format SAK.txt: standardize document format rpmsg.txt: standardize document format robust-futexes.txt: standardize document format ...
231 lines
11 KiB
Plaintext
231 lines
11 KiB
Plaintext
===========
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NTB Drivers
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===========
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NTB (Non-Transparent Bridge) is a type of PCI-Express bridge chip that connects
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the separate memory systems of two or more computers to the same PCI-Express
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fabric. Existing NTB hardware supports a common feature set: doorbell
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registers and memory translation windows, as well as non common features like
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scratchpad and message registers. Scratchpad registers are read-and-writable
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registers that are accessible from either side of the device, so that peers can
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exchange a small amount of information at a fixed address. Message registers can
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be utilized for the same purpose. Additionally they are provided with with
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special status bits to make sure the information isn't rewritten by another
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peer. Doorbell registers provide a way for peers to send interrupt events.
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Memory windows allow translated read and write access to the peer memory.
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NTB Core Driver (ntb)
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=====================
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The NTB core driver defines an api wrapping the common feature set, and allows
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clients interested in NTB features to discover NTB the devices supported by
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hardware drivers. The term "client" is used here to mean an upper layer
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component making use of the NTB api. The term "driver," or "hardware driver,"
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is used here to mean a driver for a specific vendor and model of NTB hardware.
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NTB Client Drivers
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==================
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NTB client drivers should register with the NTB core driver. After
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registering, the client probe and remove functions will be called appropriately
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as ntb hardware, or hardware drivers, are inserted and removed. The
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registration uses the Linux Device framework, so it should feel familiar to
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anyone who has written a pci driver.
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NTB Typical client driver implementation
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----------------------------------------
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Primary purpose of NTB is to share some peace of memory between at least two
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systems. So the NTB device features like Scratchpad/Message registers are
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mainly used to perform the proper memory window initialization. Typically
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there are two types of memory window interfaces supported by the NTB API:
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inbound translation configured on the local ntb port and outbound translation
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configured by the peer, on the peer ntb port. The first type is
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depicted on the next figure
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Inbound translation:
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Memory: Local NTB Port: Peer NTB Port: Peer MMIO:
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____________
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| dma-mapped |-ntb_mw_set_trans(addr) |
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| memory | _v____________ | ______________
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| (addr) |<======| MW xlat addr |<====| MW base addr |<== memory-mapped IO
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|------------| |--------------| | |--------------|
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So typical scenario of the first type memory window initialization looks:
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1) allocate a memory region, 2) put translated address to NTB config,
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3) somehow notify a peer device of performed initialization, 4) peer device
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maps corresponding outbound memory window so to have access to the shared
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memory region.
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The second type of interface, that implies the shared windows being
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initialized by a peer device, is depicted on the figure:
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Outbound translation:
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Memory: Local NTB Port: Peer NTB Port: Peer MMIO:
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____________ ______________
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| dma-mapped | | | MW base addr |<== memory-mapped IO
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| memory | | |--------------|
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| (addr) |<===================| MW xlat addr |<-ntb_peer_mw_set_trans(addr)
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|------------| | |--------------|
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Typical scenario of the second type interface initialization would be:
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1) allocate a memory region, 2) somehow deliver a translated address to a peer
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device, 3) peer puts the translated address to NTB config, 4) peer device maps
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outbound memory window so to have access to the shared memory region.
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As one can see the described scenarios can be combined in one portable
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algorithm.
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Local device:
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1) Allocate memory for a shared window
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2) Initialize memory window by translated address of the allocated region
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(it may fail if local memory window initialization is unsupported)
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3) Send the translated address and memory window index to a peer device
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Peer device:
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1) Initialize memory window with retrieved address of the allocated
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by another device memory region (it may fail if peer memory window
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initialization is unsupported)
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2) Map outbound memory window
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In accordance with this scenario, the NTB Memory Window API can be used as
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follows:
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Local device:
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1) ntb_mw_count(pidx) - retrieve number of memory ranges, which can
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be allocated for memory windows between local device and peer device
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of port with specified index.
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2) ntb_get_align(pidx, midx) - retrieve parameters restricting the
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shared memory region alignment and size. Then memory can be properly
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allocated.
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3) Allocate physically contiguous memory region in compliance with
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restrictions retrieved in 2).
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4) ntb_mw_set_trans(pidx, midx) - try to set translation address of
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the memory window with specified index for the defined peer device
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(it may fail if local translated address setting is not supported)
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5) Send translated base address (usually together with memory window
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number) to the peer device using, for instance, scratchpad or message
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registers.
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Peer device:
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1) ntb_peer_mw_set_trans(pidx, midx) - try to set received from other
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device (related to pidx) translated address for specified memory
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window. It may fail if retrieved address, for instance, exceeds
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maximum possible address or isn't properly aligned.
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2) ntb_peer_mw_get_addr(widx) - retrieve MMIO address to map the memory
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window so to have an access to the shared memory.
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Also it is worth to note, that method ntb_mw_count(pidx) should return the
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same value as ntb_peer_mw_count() on the peer with port index - pidx.
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NTB Transport Client (ntb\_transport) and NTB Netdev (ntb\_netdev)
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------------------------------------------------------------------
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The primary client for NTB is the Transport client, used in tandem with NTB
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Netdev. These drivers function together to create a logical link to the peer,
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across the ntb, to exchange packets of network data. The Transport client
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establishes a logical link to the peer, and creates queue pairs to exchange
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messages and data. The NTB Netdev then creates an ethernet device using a
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Transport queue pair. Network data is copied between socket buffers and the
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Transport queue pair buffer. The Transport client may be used for other things
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besides Netdev, however no other applications have yet been written.
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NTB Ping Pong Test Client (ntb\_pingpong)
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-----------------------------------------
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The Ping Pong test client serves as a demonstration to exercise the doorbell
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and scratchpad registers of NTB hardware, and as an example simple NTB client.
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Ping Pong enables the link when started, waits for the NTB link to come up, and
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then proceeds to read and write the doorbell scratchpad registers of the NTB.
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The peers interrupt each other using a bit mask of doorbell bits, which is
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shifted by one in each round, to test the behavior of multiple doorbell bits
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and interrupt vectors. The Ping Pong driver also reads the first local
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scratchpad, and writes the value plus one to the first peer scratchpad, each
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round before writing the peer doorbell register.
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Module Parameters:
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* unsafe - Some hardware has known issues with scratchpad and doorbell
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registers. By default, Ping Pong will not attempt to exercise such
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hardware. You may override this behavior at your own risk by setting
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unsafe=1.
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* delay\_ms - Specify the delay between receiving a doorbell
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interrupt event and setting the peer doorbell register for the next
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round.
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* init\_db - Specify the doorbell bits to start new series of rounds. A new
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series begins once all the doorbell bits have been shifted out of
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range.
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* dyndbg - It is suggested to specify dyndbg=+p when loading this module, and
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then to observe debugging output on the console.
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NTB Tool Test Client (ntb\_tool)
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--------------------------------
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The Tool test client serves for debugging, primarily, ntb hardware and drivers.
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The Tool provides access through debugfs for reading, setting, and clearing the
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NTB doorbell, and reading and writing scratchpads.
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The Tool does not currently have any module parameters.
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Debugfs Files:
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* *debugfs*/ntb\_tool/*hw*/
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A directory in debugfs will be created for each
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NTB device probed by the tool. This directory is shortened to *hw*
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below.
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* *hw*/db
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This file is used to read, set, and clear the local doorbell. Not
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all operations may be supported by all hardware. To read the doorbell,
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read the file. To set the doorbell, write `s` followed by the bits to
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set (eg: `echo 's 0x0101' > db`). To clear the doorbell, write `c`
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followed by the bits to clear.
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* *hw*/mask
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This file is used to read, set, and clear the local doorbell mask.
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See *db* for details.
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* *hw*/peer\_db
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This file is used to read, set, and clear the peer doorbell.
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See *db* for details.
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* *hw*/peer\_mask
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This file is used to read, set, and clear the peer doorbell
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mask. See *db* for details.
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* *hw*/spad
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This file is used to read and write local scratchpads. To read
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the values of all scratchpads, read the file. To write values, write a
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series of pairs of scratchpad number and value
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(eg: `echo '4 0x123 7 0xabc' > spad`
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# to set scratchpads `4` and `7` to `0x123` and `0xabc`, respectively).
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* *hw*/peer\_spad
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This file is used to read and write peer scratchpads. See
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*spad* for details.
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NTB Hardware Drivers
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====================
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NTB hardware drivers should register devices with the NTB core driver. After
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registering, clients probe and remove functions will be called.
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NTB Intel Hardware Driver (ntb\_hw\_intel)
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------------------------------------------
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The Intel hardware driver supports NTB on Xeon and Atom CPUs.
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Module Parameters:
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* b2b\_mw\_idx
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If the peer ntb is to be accessed via a memory window, then use
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this memory window to access the peer ntb. A value of zero or positive
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starts from the first mw idx, and a negative value starts from the last
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mw idx. Both sides MUST set the same value here! The default value is
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`-1`.
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* b2b\_mw\_share
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If the peer ntb is to be accessed via a memory window, and if
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the memory window is large enough, still allow the client to use the
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second half of the memory window for address translation to the peer.
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* xeon\_b2b\_usd\_bar2\_addr64
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If using B2B topology on Xeon hardware, use
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this 64 bit address on the bus between the NTB devices for the window
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at BAR2, on the upstream side of the link.
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* xeon\_b2b\_usd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
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* xeon\_b2b\_usd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
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* xeon\_b2b\_usd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
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* xeon\_b2b\_dsd\_bar2\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
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* xeon\_b2b\_dsd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
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* xeon\_b2b\_dsd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
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* xeon\_b2b\_dsd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
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