firewire: ohci: fix Agere FW643 and multiple cameras
An Agere FW643 OHCI 1.1 card works fine for video reception from one camera but fails early if receiving from two cameras. After a short while, no IR IRQ events occur and the context control register does not react anymore. This happens regardless whether both IR DMA contexts are dual-buffer or one is dual-buffer and the other packet-per-buffer. This can be worked around by disabling dual buffer DMA mode entirely. http://sourceforge.net/mailarchive/message.php?msg_name=4A7C0594.2020208%40gmail.com (Reported by Samuel Audet.) In another report (by Jonathan Cameron), an FW643 works OK with two cameras in dual buffer mode. Whether this is due to different chip revisions or different usage patterns (different video formats) is not yet clear. However, as far as the current capabilities of firewire-core's isochronous I/O interface are concerned, simply switching off dual-buffer on non-working and working FW643s alike is not a problem in practice. We only need to revisit this issue if we are going to enhance the interface, e.g. so that applications can explicitly choose modes. Reported-by:Samuel Audet <samuel.audet@gmail.com> Reported-by:
Jonathan Cameron <jic23@cam.ac.uk> Signed-off-by:
Stefan Richter <stefanr@s5r6.in-berlin.de>
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