[PATCH] ieee1394: ohci1394: increase AT req. retries, fix ack_busy_Xfrom Panasonic camcorders and others

[Stefan Richter]

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 .

Tested-by: Mathias Beilstein
Signed-off-by: Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx>
---
 drivers/ieee1394/ohci1394.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/drivers/ieee1394/ohci1394.h
===================================================================
--- linux.orig/drivers/ieee1394/ohci1394.h
+++ linux/drivers/ieee1394/ohci1394.h
@@ -26,7 +26,7 @@
 
 #define OHCI1394_DRIVER_NAME      "ohci1394"
 
-#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
 #define OHCI1394_MAX_SELF_ID_ERRORS	16

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

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