[PATCH 1/4] ALSA: hda/realtek: fix mute/micmute LEDs for HP 855 G8

[Alexander Sergeyev]

On Sat, Jan 29, 2022 at 05:47:07PM +0300, Alexander Sergeyev wrote:
> But unbind-bind problems with IO_PAGE_FAULT and "out of range cmd" are not 
> eliminated. IO_PAGE_FAULT are often logged without accompanying "out of range 
> cmd". And after adding debugging printk() I haven't managed to trigger "out 
> of range cmd" yet. But IO_PAGE_FAULT are more easily triggered.

IO_PAGE_FAULTs go away with CONFIG_IOMMU_DEFAULT_PASSTHROUGH enabled. As I 
understand, this leads to reduced DMA device isolation which is generally not 
desirable. I was initially thinking about races between some delayed code and 
io-memory pages unmapping, but first IO_PAGE_FAULTs (running non-passthrough 
iommu) happen during bind operations as well.

What is also interesting, unbind & bind consistently fails on 31th bind:

echo -n '0000:05:00.6' > /sys/bus/pci/drivers/snd_hda_intel/bind
-bash: echo: write error: No such device

And does not recover from there until a reboot.