[linux-dvb] NSLU2 dma_free_coherent issue with DIB0700 driver (and probably others)
lee.essen at nowonline.co.uk
Thu Apr 3 12:48:05 CEST 2008
Apologies if this is directed in the wrong place, as I suspect this is
more of a kernel/USB issue than a DVB driver issue, but it does have
an impact on people wanting to use this device with an NSLU2 (and I
suspect it will also be a problem with many other devices.)
I have been experimenting using a variety of DVB-T USB devices with an
NSLU2 with my ultimate aim being to build in a dual DVB-T device into
the case and use it in very much the same way as the HDHomeRun device.
Using a DTT200U based device everything worked perfectly.
Then I started playing with a DIB0700 based device (actually an Elgato
Eye-TV Diversity) and the system would just hang whenever I started
using dvbstream, I got slightly different behaviour if I tried to tune
it to an invalid frequency and eventually managed to get to a state
when I could interrupt it before it completely locked up.
It seems that the driver was flagging an issue in the ARM architecture
around not calling dma_free_coherent() with IRQ's disabled, apparently
a warning was recently added to the ARM kernel so it logs a message
and a stack trace each time ... this seemed to be happening so
frequently it effectively locked the system up.
I did a little digging, but I'm not a kernel expert at all, and it
seems that the ehci_hcd module is actually where the call is
originating rather than the DVB driver itself, so I suspect that this
will actually effect a significant number of the drivers when used on
an ARM platform.
For the purposes of testing I removed the warning (from arch/arm/mm/
consistent line 363) and everything is fine, the driver operates
perfectly and I can stream video nicely. BUT - clearly there is some
kind of issue here that needs to be resolved.
More information is available at the link below, and also I have read
comments suggesting that the issue has been discussed on the arm-
kernel mailing list but that no resolution has yet been found.
For reference I'm using 2.6.24 and have tried the most recent drivers
from linuxtv.org as well as a variety of others -- all seem to have
the same problem (which is expected if the problem is actually in the
Hope this is useful,
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