firewire: cdev: ABI documentation enhancements

Add overview documentation in Documentation/ABI/stable/firewire-cdev.

Improve the inline reference documentation in firewire-cdev.h:

  - Add /* available since kernel... */ comments to event numbers
    consistent with the comments on ioctl numbers.

  - Shorten some documentation on an event and an ioctl that are
    less interesting to current programming because there are newer
    preferable variants.

  - Spell Configuration ROM (name of an IEEE 1212 register) in
    upper case.

  - Move the dummy FW_CDEV_VERSION out of the reader's field of
    vision.  We should remove it from the header next year or so.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

Documentation/ABI/stable/firewire-cdev

@@ -0,0 +1,103 @@
+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.
+
+Users:		libraw1394
+		libdc1394
+		tools like jujuutils, fwhack, ...