Re: PCTV 290e page allocation failure

[Gianluca Gennari <gennarone@gmail.com>]

Il 03/02/2012 00:12, Devin Heitmueller ha scritto:
> On Thu, Feb 2, 2012 at 6:06 PM, Gianluca Gennari <gennarone@gmail.com> wrote:
>> Il 02/02/2012 20:07, Devin Heitmueller ha scritto:
>> Hi Devin,
>> thanks for the explanation. The CPU is MIPS based (not ARM) but I guess
>> there is not much of a difference from this point of view.
>> As I mentioned in my first reply, I never had this kind of errors when I
>> was using a dvb-usb USB stick. Now I'm trying to replicate the problem
>> with a Terratec Hybrid XS (em28xx-dvb + zl10353 + xc2028), and so far
>> I've stressed it for a few hours without problems. We will see in a day
>> or two if I can make it fail in the same way.
> 
> I'm pretty sure this will happen under MIPS as well.  That said, you
> will typically hit this condition if you stop streaming and then
> restart it several hours into operation.  In other words, make sure
> you're not just watching/streaming video for a few hours and thinking
> you're stressing the particular use case.  You need to stop/start to
> hit it.

Yes, I've been switching between the mediaplayer (playing some 1080p mkv
file to stress the memory) and the USB tuner, but so far so good.
But I need to run the test longer to draw some conclusion.

> I haven't looked that closely at dvb_usb's memory allocation strategy.
>  Perhaps it allocates the memory up front, or perhaps it doesn't
> demand coherent memory (something which will work on x86 and maybe
> MIPS, but will cause an immediate panic on ARM).
> 
> I've run into this issue myself on an embedded target with em28xx and
> ARM.  I plan on hacking a fix to statically allocate the buffers at
> driver init, but I cannot imagine that being a change that would be
> accepted into the upstream kernel.

If you have some patch that you want to share, I will be happy to test it.

> It probably makes sense to figure out whether MIPS requires coherent
> memory like ARM does.  If it doesn't then you can probably just hack
> your copy of the em28xx driver to not ask for coherent memory.  If it
> does require coherent memory, then you'll probably need to allocate
> the memory up front.
> 

Interesting suggestion. I have really no idea if MIPS really requires
coherent memory in this case. I may try to hack it and see what happens.

Thank you very much for the detailed explanation.

Regards,
Gianluca

> Cheers,
> 
> Devin
>