linux-imx/Documentation/ABI/stable/firewire-cdev

What: /dev/fw[0-9]+ Date: May 2007 KernelVersion: 2.6.22 Contact: linux1394-devel@lists.sourceforge.net Description: The character device files /dev/fw* are the interface between firewire-core and IEEE 1394 device drivers implemented in userspace. The ioctl(2)- and read(2)-based ABI is defined and documented in <linux/firewire-cdev.h>.

	This ABI offers most of the features which firewire-core also
	exposes to kernelspace IEEE 1394 drivers.

	Each /dev/fw* is associated with one IEEE 1394 node, which can
	be remote or local nodes.  Operations on a /dev/fw* file have
	different scope:

	  - The 1394 node which is associated with the file:

		  - Asynchronous request transmission
		  - Get the Configuration ROM
		  - Query node ID
		  - Query maximum speed of the path between this node
		    and local node

	  - The 1394 bus (i.e. "card") to which the node is attached to:

		  - Isochronous stream transmission and reception
		  - Asynchronous stream transmission and reception
		  - Asynchronous broadcast request transmission
		  - PHY packet transmission and reception
		  - Allocate, reallocate, deallocate isochronous
		    resources (channels, bandwidth) at the bus's IRM
		  - Query node IDs of local node, root node, IRM, bus
		    manager
		  - Query cycle time
		  - Bus reset initiation, bus reset event reception

	  - All 1394 buses:

		  - Allocation of IEEE 1212 address ranges on the local
		    link layers, reception of inbound requests to such
		    an address range, asynchronous response transmission
		    to inbound requests
		  - Addition of descriptors or directories to the local
		    nodes' Configuration ROM

	Due to the different scope of operations and in order to let
	userland implement different access permission models, some
	operations are restricted to /dev/fw* files that are associated
	with a local node:

		  - Addition of descriptors or directories to the local
		    nodes' Configuration ROM
		  - PHY packet transmission and reception

	A /dev/fw* file remains associated with one particular node
	during its entire life time.  Bus topology changes, and hence
	node ID changes, are tracked by firewire-core.  ABI users do not
	need to be aware of topology.

	The following file operations are supported:

	open(2)
	    Currently the only useful flags are O_RDWR.

	ioctl(2)
	    Initiate various actions.  Some take immediate effect, others
	    are performed asynchronously while or after the ioctl returns.
	    See the inline documentation in <linux/firewire-cdev.h> for
	    descriptions of all ioctls.

	poll(2), select(2), epoll_wait(2) etc.
	    Watch for events to become available to be read.

	read(2)
	    Receive various events.  There are solicited events like
	    outbound asynchronous transaction completion or isochronous
	    buffer completion, and unsolicited events such as bus resets,
	    request reception, or PHY packet reception.  Always use a read
	    buffer which is large enough to receive the largest event that
	    could ever arrive.  See <linux/firewire-cdev.h> for descriptions
	    of all event types and for which ioctls affect reception of
	    events.

	mmap(2)
	    Allocate a DMA buffer for isochronous reception or transmission
	    and map it into the process address space.  The arguments should
	    be used as follows:  addr = NULL, length = the desired buffer
	    size, i.e. number of packets times size of largest packet,
	    prot = at least PROT_READ for reception and at least PROT_WRITE
	    for transmission, flags = MAP_SHARED, fd = the handle to the
	    /dev/fw*, offset = 0.

	Isochronous reception works in packet-per-buffer fashion except
	for multichannel reception which works in buffer-fill mode.

	munmap(2)
	    Unmap the isochronous I/O buffer from the process address space.

	close(2)
	    Besides stopping and freeing I/O contexts that were associated
	    with the file descriptor, back out any changes to the local
	    nodes' Configuration ROM.  Deallocate isochronous channels and
	    bandwidth at the IRM that were marked for kernel-assisted
	    re- and deallocation.

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