HDA controllers and MSI support.

[Alexander Motin]

Hi.

I have tried and found that my ICH8-based system successfully supports 
Message Signaled Interrupts on HDA controller. It allows to avoid 
interrupt sharing and in theory gives some performance benefits.

It is now disabled in driver by default, but can be enabled via 
hint.hdac.%d.msi device.hints control. You can see that MSI is in use if 
your hdacX device uses interrupt vector above 255.

I am thinking, shouldn't we enable this feature by default?

There should be no problem with both supporting and nonsupporting 
hardware. There could be only problems with broken hardware declaring 
fake features. So I would like to know, is there any of such cases for 
HDA hardware or not?

-- 
Alexander Motin