ALSA: hda - Update document about MSI and interrupts

Interrupt Handling

~~~~~~~~~~~~~~~~~~

In rare but some cases, the interrupt isn't properly handled as

default.  You would notice this by the DMA transfer error reported by

ALSA PCM core, for example.  Using MSI might help in such a case.

Pass `enable_msi=1` option for enabling MSI.

HD-audio driver uses MSI as default (if available) since 2.6.33

kernel as MSI works better on some machines, and in general, it's

better for performance.  However, Nvidia controllers showed bad

regressions with MSI (especially in a combination with AMD chipset),

thus we disabled MSI for them.

There seem also still other devices that don't work with MSI.  If you

see a regression wrt the sound quality (stuttering, etc) or a lock-up

in the recent kernel, try to pass `enable_msi=0` option to disable

MSI.  If it works, you can add the known bad device to the blacklist

defined in hda_intel.c.  In such a case, please report and give the

patch back to the upstream developer. 

HD-AUDIO CODEC