mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-10-29 23:53:32 +00:00
59bc64f0d0
In order to make it easier to parse and produce the right output, add some extra blank lines. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
236 lines
11 KiB
Text
236 lines
11 KiB
Text
===========
|
|
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 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*.
|