Re: Make b43 driver fall back gracefully to PIO mode after fatal DMA errors

[Larry Finger <Larry.Finger@lwfinger.net>]

On 02/26/2010 02:50 PM, Linus Torvalds wrote:
> 
> 
> On Fri, 26 Feb 2010, Gábor Stefanik wrote:
>>
>> Does actually enabling mmiotrace fix it for you too?
> 
> I haven't seen the report. What do you need to do? Certainly just enabling 
> CONFIG_MMIOTRACE does nothing, but I'd not expect it to - I'd expect that 
> you have to actually do the tracing itself.
> 
> So if somebody has a recipe for me to test actual tracing of the module, I 
> can try to see if it makes a difference for me.

If you do the following (as root):

modprobe -r b43
echo 6400 > /sys/kernel/debug/tracing/buffer_size_kb
echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
modprobe b43

do some network activity, then

echo nop > /sys/kernel/debug/tracing/current_tracer
sleep 1
killproc cat

That should be a good enough test. If your machine behaves the same as has been
reported, you should see a DMA error at the point that tracing is turned off.

Larry