[PATCH] firewire: ohci: increase AT req. retries, fix ack_busy_X from Panasonic camcorders and others

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

Camcorders have a tendency to fail read requests to their config ROM and
write request to their FCP command register with ack_busy_X.  This has
become a problem with newer kernels and especially Panasonic camcorders,
causing AV/C in dvgrab and kino to fail.  Dvgrab for example frequently
logs "send oops"; kino reports loss of AV/C control.  I suspect that
lower CPU scheduling latencies in newer kernels made this issue more
prominent in current kernels.

According to
https://sourceforge.net/tracker/?func=detail&atid=114103&aid=2492640&group_id=14103
this can be fixed by configuring the FireWire controller for more
hardware retries for request transmission; these retries are evidently
more successful than libavc1394's own retry loop (typically 3 tries on
top of hardware retries).

Presumably the same issue has been reported at
https://bugzilla.redhat.com/show_bug.cgi?id=449252 and
https://bugzilla.redhat.com/show_bug.cgi?id=477279 .

In a quick test with a JVC camcorder (which didn't malfunction like the
reported camcorders), this change decreased the number of ack_busy_X
from 16 in three runs of dvgrab to 4 in three runs of the same capture
duration.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
---
 drivers/firewire/fw-ohci.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/drivers/firewire/fw-ohci.c
===================================================================
--- linux.orig/drivers/firewire/fw-ohci.c
+++ linux/drivers/firewire/fw-ohci.c
@@ -227,7 +227,7 @@ static inline struct fw_ohci *fw_ohci(st
 #define CONTEXT_DEAD	0x0800
 #define CONTEXT_ACTIVE	0x0400
 
-#define OHCI1394_MAX_AT_REQ_RETRIES	0x2
+#define OHCI1394_MAX_AT_REQ_RETRIES	0xf
 #define OHCI1394_MAX_AT_RESP_RETRIES	0x2
 #define OHCI1394_MAX_PHYS_RESP_RETRIES	0x8
 

-- 
Stefan Richter
-=====-==--= ---= =-=--
http://arcgraph.de/sr/