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firewire: cdev: iso packet documentation

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Add the missing documentation for iso packets.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
This commit is contained in:
Clemens Ladisch 2010-03-31 16:26:52 +02:00 committed by Stefan Richter
parent 9cac00b8f0
commit aa6fec3cde
1 changed files with 32 additions and 5 deletions
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37
include/linux/firewire-cdev.h
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@ -438,7 +438,7 @@ struct fw_cdev_remove_descriptor {
* @type: %FW_CDEV_ISO_CONTEXT_TRANSMIT or %FW_CDEV_ISO_CONTEXT_RECEIVE
* @header_size: Header size to strip for receive contexts
* @channel: Channel to bind to
* @speed: Speed to transmit at
* @speed: Speed for transmit contexts
* @closure: To be returned in &fw_cdev_event_iso_interrupt
* @handle: Handle to context, written back by kernel
*
@ -451,6 +451,9 @@ struct fw_cdev_remove_descriptor {
* If a context was successfully created, the kernel writes back a handle to the
* context, which must be passed in for subsequent operations on that context.
*
* For receive contexts, @header_size must be at least 4 and must be a multiple
* of 4.
*
* Note that the effect of a @header_size > 4 depends on
* &fw_cdev_get_info.version, as documented at &fw_cdev_event_iso_interrupt.
*/
@ -481,10 +484,34 @@ struct fw_cdev_create_iso_context {
*
* &struct fw_cdev_iso_packet is used to describe isochronous packet queues.
*
* Use the FW_CDEV_ISO_ macros to fill in @control. The sy and tag fields are
* specified by IEEE 1394a and IEC 61883.
* Use the FW_CDEV_ISO_ macros to fill in @control.
*
* FIXME - finish this documentation
* For transmit packets, the header length must be a multiple of 4 and specifies
* the numbers of bytes in @header that will be prepended to the packet's
* payload; these bytes are copied into the kernel and will not be accessed
* after the ioctl has returned. The sy and tag fields are copied to the iso
* packet header (these fields are specified by IEEE 1394a and IEC 61883-1).
* The skip flag specifies that no packet is to be sent in a frame; when using
* this, all other fields except the interrupt flag must be zero.
*
* For receive packets, the header length must be a multiple of the context's
* header size; if the header length is larger than the context's header size,
* multiple packets are queued for this entry. The sy and tag fields are
* ignored. If the sync flag is set, the context drops all packets until
* a packet with a matching sy field is received (the sync value to wait for is
* specified in the &fw_cdev_start_iso structure). The payload length defines
* how many payload bytes can be received for one packet (in addition to payload
* quadlets that have been defined as headers and are stripped and returned in
* the &fw_cdev_event_iso_interrupt structure). If more bytes are received, the
* additional bytes are dropped. If less bytes are received, the remaining
* bytes in this part of the payload buffer will not be written to, not even by
* the next packet, i.e., packets received in consecutive frames will not
* necessarily be consecutive in memory. If an entry has queued multiple
* packets, the payload length is divided equally among them.
*
* When a packet with the interrupt flag set has been completed, the
* &fw_cdev_event_iso_interrupt event will be sent. An entry that has queued
* multiple receive packets is completed when its last packet is completed.
*/
struct fw_cdev_iso_packet {
__u32 control;
@ -501,7 +528,7 @@ struct fw_cdev_iso_packet {
* Queue a number of isochronous packets for reception or transmission.
* This ioctl takes a pointer to an array of &fw_cdev_iso_packet structs,
* which describe how to transmit from or receive into a contiguous region
* of a mmap()'ed payload buffer. As part of the packet descriptors,
* of a mmap()'ed payload buffer. As part of transmit packet descriptors,
* a series of headers can be supplied, which will be prepended to the
* payload during DMA.
*