Re: [PATCH 0/2] PCI/AER: Consistently use _OSC to determine who owns AER

[Sinan Kaya]

On 11/20/2018 4:42 PM, Keith Busch wrote:
> How does that work? If the OS takes control, it sets up MSIs that FW don't
> react to, and disables system errors through PCIe Root Control. Aren't
> those sys errs the mechanism FW knows it has something to do, which
> means the OS can effectively fence it off?

I think this is all implementation detail and doesn't necessarily apply
to all firmware-first implementation flavors.

Assumptions are:
1. both FW and OS are listening to MSI interrupts
2. FW monitors the system errors

Some FF implementation could route the AER interrupt to a higher privilege
level. Some other implementation could use INTx or a side-band channel interrupt
for firmware-interrupt too.

I have seen all 3 except MSI :) and also firmware never monitored the system
error bits. I was curious if anybody ever used those legacy bits. Now, I know
someone is using it.