Documentation/ABI/stable/firewire-cdev

   1 What:           /dev/fw[0-9]+
   2 Date:           May 2007
   3 KernelVersion:  2.6.22
   4 Contact:        linux1394-devel@lists.sourceforge.net
   5 Description:
   6                 The character device files /dev/fw* are the interface between
   7                 firewire-core and IEEE 1394 device drivers implemented in
   8                 userspace.  The ioctl(2)- and read(2)-based ABI is defined and
   9                 documented in <linux/firewire-cdev.h>.
  10
  11                 This ABI offers most of the features which firewire-core also
  12                 exposes to kernelspace IEEE 1394 drivers.
  13
  14                 Each /dev/fw* is associated with one IEEE 1394 node, which can
  15                 be remote or local nodes.  Operations on a /dev/fw* file have
  16                 different scope:
  17                   - The 1394 node which is associated with the file:
  18                           - Asynchronous request transmission
  19                           - Get the Configuration ROM
  20                           - Query node ID
  21                           - Query maximum speed of the path between this node
  22                             and local node
  23                   - The 1394 bus (i.e. "card") to which the node is attached to:
  24                           - Isochronous stream transmission and reception
  25                           - Asynchronous stream transmission and reception
  26                           - Asynchronous broadcast request transmission
  27                           - PHY packet transmission and reception
  28                           - Allocate, reallocate, deallocate isochronous
  29                             resources (channels, bandwidth) at the bus's IRM
  30                           - Query node IDs of local node, root node, IRM, bus
  31                             manager
  32                           - Query cycle time
  33                           - Bus reset initiation, bus reset event reception
  34                   - All 1394 buses:
  35                           - Allocation of IEEE 1212 address ranges on the local
  36                             link layers, reception of inbound requests to such
  37                             an address range, asynchronous response transmission
  38                             to inbound requests
  39                           - Addition of descriptors or directories to the local
  40                             nodes' Configuration ROM
  41
  42                 Due to the different scope of operations and in order to let
  43                 userland implement different access permission models, some
  44                 operations are restricted to /dev/fw* files that are associated
  45                 with a local node:
  46                           - Addition of descriptors or directories to the local
  47                             nodes' Configuration ROM
  48                           - PHY packet transmission and reception
  49
  50                 A /dev/fw* file remains associated with one particular node
  51                 during its entire life time.  Bus topology changes, and hence
  52                 node ID changes, are tracked by firewire-core.  ABI users do not
  53                 need to be aware of topology.
  54
  55                 The following file operations are supported:
  56
  57                 open(2)
  58                 Currently the only useful flags are O_RDWR.
  59
  60                 ioctl(2)
  61                 Initiate various actions.  Some take immediate effect, others
  62                 are performed asynchronously while or after the ioctl returns.
  63                 See the inline documentation in <linux/firewire-cdev.h> for
  64                 descriptions of all ioctls.
  65
  66                 poll(2), select(2), epoll_wait(2) etc.
  67                 Watch for events to become available to be read.
  68
  69                 read(2)
  70                 Receive various events.  There are solicited events like
  71                 outbound asynchronous transaction completion or isochronous
  72                 buffer completion, and unsolicited events such as bus resets,
  73                 request reception, or PHY packet reception.  Always use a read
  74                 buffer which is large enough to receive the largest event that
  75                 could ever arrive.  See <linux/firewire-cdev.h> for descriptions
  76                 of all event types and for which ioctls affect reception of
  77                 events.
  78
  79                 mmap(2)
  80                 Allocate a DMA buffer for isochronous reception or transmission
  81                 and map it into the process address space.  The arguments should
  82                 be used as follows:  addr = NULL, length = the desired buffer
  83                 size, i.e. number of packets times size of largest packet,
  84                 prot = at least PROT_READ for reception and at least PROT_WRITE
  85                 for transmission, flags = MAP_SHARED, fd = the handle to the
  86                 /dev/fw*, offset = 0.
  87
  88                 Isochronous reception works in packet-per-buffer fashion except
  89                 for multichannel reception which works in buffer-fill mode.
  90
  91                 munmap(2)
  92                 Unmap the isochronous I/O buffer from the process address space.
  93
  94                 close(2)
  95                 Besides stopping and freeing I/O contexts that were associated
  96                 with the file descriptor, back out any changes to the local
  97                 nodes' Configuration ROM.  Deallocate isochronous channels and
  98                 bandwidth at the IRM that were marked for kernel-assisted
  99                 re- and deallocation.
 100
 101 Users:          libraw1394
 102                 libdc1394
 103                 tools like jujuutils, fwhack, ...