firewire: add isochronous multichannel reception

This adds the DMA context programming and userspace ABI for multichannel
reception, i.e. for listening on multiple channel numbers by means of a
single DMA context.

The use case is reception of more streams than there are IR DMA units
offered by the link layer.  This is already implemented by the older
ohci1394 + ieee1394 + raw1394 stack.  And as discussed recently on
linux1394-devel, this feature is occasionally used in practice.

The big drawbacks of this mode are that buffer layout and interrupt
generation necessarily differ from single-channel reception:  Headers
and trailers are not stripped from packets, packets are not aligned with
buffer chunks, interrupts are per buffer chunk, not per packet.

These drawbacks also cause a rather hefty code footprint to support this
rarely used OHCI-1394 feature.  (367 lines added, among them 94 lines of
added userspace ABI documentation.)

This implementation enforces that a multichannel reception context may
only listen to channels to which no single-channel context on the same
link layer is presently listening to.  OHCI-1394 would allow to overlay
single-channel contexts by the multi-channel context, but this would be
a departure from the present first-come-first-served policy of IR
context creation.

The implementation is heavily based on an earlier one by Jay Fenlason.
Thanks Jay.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/firewire/core.h b/drivers/firewire/core.h
index 28621e4..e6239f9 100644
--- a/drivers/firewire/core.h
+++ b/drivers/firewire/core.h
@@ -90,6 +90,8 @@ struct fw_card_driver {
 	int (*start_iso)(struct fw_iso_context *ctx,
 			 s32 cycle, u32 sync, u32 tags);
 
+	int (*set_iso_channels)(struct fw_iso_context *ctx, u64 *channels);
+
 	int (*queue_iso)(struct fw_iso_context *ctx,
 			 struct fw_iso_packet *packet,
 			 struct fw_iso_buffer *buffer,