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In isochronous transmit DMA descriptors, link the skip address pointer back to the descriptor itself. When a cycle is lost, the controller will send the packet in the next cycle, instead of terminating the entire DMA program. There are two reasons for this: * This behaviour is compatible with the old IEEE1394 stack. Old applications would not expect the DMA program to stop in this case. * Since the OHCI driver does not report any uncompleted packets, the context would stop silently; clients would not have any chance to detect and handle this error without a watchdog timer. Signed-off-by: Clemens Ladisch <clemens@ladisch.de> Pieter Palmers notes: "The reason I added this retry behavior to the old stack is because some cards now and then fail to send a packet (e.g. the o2micro card in my dell laptop). I couldn't figure out why exactly this happens, my best guess is that the card cannot fetch the payload data on time. This happens much more frequently when sending large packets, which leads me to suspect that there are some contention issues with the DMA that fills the transmit FIFO. In the old stack it was a pretty critical issue as it resulted in a freeze of the userspace application. The omission of a packet doesn't necessarily have to be an issue. E.g. in IEC61883 streams the DBC field can be used to detect discontinuities in the stream. So as long as the other side doesn't bail when no [packet] is present in a cycle, there is not really a problem. I'm not convinced though that retrying is the proper solution, but it is simple and effective for what it had to do. And I think there are no reasons not to do it this way. Userspace can still detect this by checking the cycle the descriptor was sent in." Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (changelog, comment) |
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| .. | ||
| core-card.c | ||
| core-cdev.c | ||
| core-device.c | ||
| core-iso.c | ||
| core-topology.c | ||
| core-transaction.c | ||
| core.h | ||
| Kconfig | ||
| Makefile | ||
| net.c | ||
| ohci.c | ||
| ohci.h | ||
| sbp2.c | ||