[Xen-devel] pvops dom0: no sound after boot; possibly caused by swiotlb
Software: xen 3.4.1, lastest xen/master (version 188.8.131.52), both 32bit
Hardware: Intel Core2Duo System
Realtek ALC888 soundchip
When playing audio in dom0 there are just "knock" sounds.
After rmmod the kernel-module for the soundcard (snd-hda-intel) and oss modules
(snd-seq-oss and snd-seq-pcm) and inserting them with modprobe again makes the
sound work. Doing that only with snd-hda-intel doesnt help.
I compiled the sound-modules directly into the kernel but that didnt changed
This problem doesnt appear with the gentoo-dom0 patches for kernel 2.6.31 so it
looks like a pvops dom0 problem.
Strangely that problem doesnt appear on another system with the same
xen-version and the exactly same kernel. Main-difference is that the other
system is a 2-core AMD-system with 2 GB Ram and a different soundcard.
But starting the domU with only 2 GB didnt made any difference.
It finally turns out that when the sound-modules are loaded after a pv-domU is
started the sound in domU works fine from the beginning.
As i suspected a problem in the memory-layout that got "fixed" by the start of
a PV-domU i started the domU with different memory-sizes and found out that the
sound works fine if the domU is started with at least 66 MB. Everything under
that and there is no sound (even the knock-sound is not there)
The first thing i found that had could have to do with the 66 MB was the 64 MB
swiotlb buffer. To check that this is really the problem i changed the code in
arch/x86/xen/pci-swiotlb.c and lowered the allocated buffer to 32MB. After that
change the sound worked from the beginning when the domU was started with less
then 66 MB.
>From here i dont know at the moment how to investigate that problem further
Which logs should i post that could help to find the problem?
What further steps could/should i do to investigate that myself?
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