--- /dev/null
+===========
+NTB Drivers
+===========
+
+NTB (Non-Transparent Bridge) is a type of PCI-Express bridge chip that connects
+the separate memory systems of two or more computers to the same PCI-Express
+fabric. Existing NTB hardware supports a common feature set: doorbell
+registers and memory translation windows, as well as non common features like
+scratchpad and message registers. Scratchpad registers are read-and-writable
+registers that are accessible from either side of the device, so that peers can
+exchange a small amount of information at a fixed address. Message registers can
+be utilized for the same purpose. Additionally they are provided with with
+special status bits to make sure the information isn't rewritten by another
+peer. Doorbell registers provide a way for peers to send interrupt events.
+Memory windows allow translated read and write access to the peer memory.
+
+NTB Core Driver (ntb)
+=====================
+
+The NTB core driver defines an api wrapping the common feature set, and allows
+clients interested in NTB features to discover NTB the devices supported by
+hardware drivers. The term "client" is used here to mean an upper layer
+component making use of the NTB api. The term "driver," or "hardware driver,"
+is used here to mean a driver for a specific vendor and model of NTB hardware.
+
+NTB Client Drivers
+==================
+
+NTB client drivers should register with the NTB core driver. After
+registering, the client probe and remove functions will be called appropriately
+as ntb hardware, or hardware drivers, are inserted and removed. The
+registration uses the Linux Device framework, so it should feel familiar to
+anyone who has written a pci driver.
+
+NTB Typical client driver implementation
+----------------------------------------
+
+Primary purpose of NTB is to share some peace of memory between at least two
+systems. So the NTB device features like Scratchpad/Message registers are
+mainly used to perform the proper memory window initialization. Typically
+there are two types of memory window interfaces supported by the NTB API:
+inbound translation configured on the local ntb port and outbound translation
+configured by the peer, on the peer ntb port. The first type is
+depicted on the next figure::
+
+ Inbound translation:
+
+ Memory: Local NTB Port: Peer NTB Port: Peer MMIO:
+ ____________
+ | dma-mapped |-ntb_mw_set_trans(addr) |
+ | memory | _v____________ | ______________
+ | (addr) |<======| MW xlat addr |<====| MW base addr |<== memory-mapped IO
+ |------------| |--------------| | |--------------|
+
+So typical scenario of the first type memory window initialization looks:
+1) allocate a memory region, 2) put translated address to NTB config,
+3) somehow notify a peer device of performed initialization, 4) peer device
+maps corresponding outbound memory window so to have access to the shared
+memory region.
+
+The second type of interface, that implies the shared windows being
+initialized by a peer device, is depicted on the figure::
+
+ Outbound translation:
+
+ Memory: Local NTB Port: Peer NTB Port: Peer MMIO:
+ ____________ ______________
+ | dma-mapped | | | MW base addr |<== memory-mapped IO
+ | memory | | |--------------|
+ | (addr) |<===================| MW xlat addr |<-ntb_peer_mw_set_trans(addr)
+ |------------| | |--------------|
+
+Typical scenario of the second type interface initialization would be:
+1) allocate a memory region, 2) somehow deliver a translated address to a peer
+device, 3) peer puts the translated address to NTB config, 4) peer device maps
+outbound memory window so to have access to the shared memory region.
+
+As one can see the described scenarios can be combined in one portable
+algorithm.
+
+ Local device:
+ 1) Allocate memory for a shared window
+ 2) Initialize memory window by translated address of the allocated region
+ (it may fail if local memory window initialization is unsupported)
+ 3) Send the translated address and memory window index to a peer device
+
+ Peer device:
+ 1) Initialize memory window with retrieved address of the allocated
+ by another device memory region (it may fail if peer memory window
+ initialization is unsupported)
+ 2) Map outbound memory window
+
+In accordance with this scenario, the NTB Memory Window API can be used as
+follows:
+
+ Local device:
+ 1) ntb_mw_count(pidx) - retrieve number of memory ranges, which can
+ be allocated for memory windows between local device and peer device
+ of port with specified index.
+ 2) ntb_get_align(pidx, midx) - retrieve parameters restricting the
+ shared memory region alignment and size. Then memory can be properly
+ allocated.
+ 3) Allocate physically contiguous memory region in compliance with
+ restrictions retrieved in 2).
+ 4) ntb_mw_set_trans(pidx, midx) - try to set translation address of
+ the memory window with specified index for the defined peer device
+ (it may fail if local translated address setting is not supported)
+ 5) Send translated base address (usually together with memory window
+ number) to the peer device using, for instance, scratchpad or message
+ registers.
+
+ Peer device:
+ 1) ntb_peer_mw_set_trans(pidx, midx) - try to set received from other
+ device (related to pidx) translated address for specified memory
+ window. It may fail if retrieved address, for instance, exceeds
+ maximum possible address or isn't properly aligned.
+ 2) ntb_peer_mw_get_addr(widx) - retrieve MMIO address to map the memory
+ window so to have an access to the shared memory.
+
+Also it is worth to note, that method ntb_mw_count(pidx) should return the
+same value as ntb_peer_mw_count() on the peer with port index - pidx.
+
+NTB Transport Client (ntb\_transport) and NTB Netdev (ntb\_netdev)
+------------------------------------------------------------------
+
+The primary client for NTB is the Transport client, used in tandem with NTB
+Netdev. These drivers function together to create a logical link to the peer,
+across the ntb, to exchange packets of network data. The Transport client
+establishes a logical link to the peer, and creates queue pairs to exchange
+messages and data. The NTB Netdev then creates an ethernet device using a
+Transport queue pair. Network data is copied between socket buffers and the
+Transport queue pair buffer. The Transport client may be used for other things
+besides Netdev, however no other applications have yet been written.
+
+NTB Ping Pong Test Client (ntb\_pingpong)
+-----------------------------------------
+
+The Ping Pong test client serves as a demonstration to exercise the doorbell
+and scratchpad registers of NTB hardware, and as an example simple NTB client.
+Ping Pong enables the link when started, waits for the NTB link to come up, and
+then proceeds to read and write the doorbell scratchpad registers of the NTB.
+The peers interrupt each other using a bit mask of doorbell bits, which is
+shifted by one in each round, to test the behavior of multiple doorbell bits
+and interrupt vectors. The Ping Pong driver also reads the first local
+scratchpad, and writes the value plus one to the first peer scratchpad, each
+round before writing the peer doorbell register.
+
+Module Parameters:
+
+* unsafe - Some hardware has known issues with scratchpad and doorbell
+ registers. By default, Ping Pong will not attempt to exercise such
+ hardware. You may override this behavior at your own risk by setting
+ unsafe=1.
+* delay\_ms - Specify the delay between receiving a doorbell
+ interrupt event and setting the peer doorbell register for the next
+ round.
+* init\_db - Specify the doorbell bits to start new series of rounds. A new
+ series begins once all the doorbell bits have been shifted out of
+ range.
+* dyndbg - It is suggested to specify dyndbg=+p when loading this module, and
+ then to observe debugging output on the console.
+
+NTB Tool Test Client (ntb\_tool)
+--------------------------------
+
+The Tool test client serves for debugging, primarily, ntb hardware and drivers.
+The Tool provides access through debugfs for reading, setting, and clearing the
+NTB doorbell, and reading and writing scratchpads.
+
+The Tool does not currently have any module parameters.
+
+Debugfs Files:
+
+* *debugfs*/ntb\_tool/*hw*/
+ A directory in debugfs will be created for each
+ NTB device probed by the tool. This directory is shortened to *hw*
+ below.
+* *hw*/db
+ This file is used to read, set, and clear the local doorbell. Not
+ all operations may be supported by all hardware. To read the doorbell,
+ read the file. To set the doorbell, write `s` followed by the bits to
+ set (eg: `echo 's 0x0101' > db`). To clear the doorbell, write `c`
+ followed by the bits to clear.
+* *hw*/mask
+ This file is used to read, set, and clear the local doorbell mask.
+ See *db* for details.
+* *hw*/peer\_db
+ This file is used to read, set, and clear the peer doorbell.
+ See *db* for details.
+* *hw*/peer\_mask
+ This file is used to read, set, and clear the peer doorbell
+ mask. See *db* for details.
+* *hw*/spad
+ This file is used to read and write local scratchpads. To read
+ the values of all scratchpads, read the file. To write values, write a
+ series of pairs of scratchpad number and value
+ (eg: `echo '4 0x123 7 0xabc' > spad`
+ # to set scratchpads `4` and `7` to `0x123` and `0xabc`, respectively).
+* *hw*/peer\_spad
+ This file is used to read and write peer scratchpads. See
+ *spad* for details.
+
++NTB MSI Test Client (ntb\_msi\_test)
++------------------------------------
++
++The MSI test client serves to test and debug the MSI library which
++allows for passing MSI interrupts across NTB memory windows. The
++test client is interacted with through the debugfs filesystem:
++
++* *debugfs*/ntb\_tool/*hw*/
++ A directory in debugfs will be created for each
++ NTB device probed by the tool. This directory is shortened to *hw*
++ below.
++* *hw*/port
++ This file describes the local port number
++* *hw*/irq*_occurrences
++ One occurrences file exists for each interrupt and, when read,
++ returns the number of times the interrupt has been triggered.
++* *hw*/peer*/port
++ This file describes the port number for each peer
++* *hw*/peer*/count
++ This file describes the number of interrupts that can be
++ triggered on each peer
++* *hw*/peer*/trigger
++ Writing an interrupt number (any number less than the value
++ specified in count) will trigger the interrupt on the
++ specified peer. That peer's interrupt's occurrence file
++ should be incremented.
++
+NTB Hardware Drivers
+====================
+
+NTB hardware drivers should register devices with the NTB core driver. After
+registering, clients probe and remove functions will be called.
+
+NTB Intel Hardware Driver (ntb\_hw\_intel)
+------------------------------------------
+
+The Intel hardware driver supports NTB on Xeon and Atom CPUs.
+
+Module Parameters:
+
+* b2b\_mw\_idx
+ If the peer ntb is to be accessed via a memory window, then use
+ this memory window to access the peer ntb. A value of zero or positive
+ starts from the first mw idx, and a negative value starts from the last
+ mw idx. Both sides MUST set the same value here! The default value is
+ `-1`.
+* b2b\_mw\_share
+ If the peer ntb is to be accessed via a memory window, and if
+ the memory window is large enough, still allow the client to use the
+ second half of the memory window for address translation to the peer.
+* xeon\_b2b\_usd\_bar2\_addr64
+ If using B2B topology on Xeon hardware, use
+ this 64 bit address on the bus between the NTB devices for the window
+ at BAR2, on the upstream side of the link.
+* xeon\_b2b\_usd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
+* xeon\_b2b\_usd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
+* xeon\_b2b\_usd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
+* xeon\_b2b\_dsd\_bar2\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
+* xeon\_b2b\_dsd\_bar4\_addr64 - See *xeon\_b2b\_bar2\_addr64*.
+* xeon\_b2b\_dsd\_bar4\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
+* xeon\_b2b\_dsd\_bar5\_addr32 - See *xeon\_b2b\_bar2\_addr64*.
projects / kernel.git / commitdiff