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Subject: Re: [PATCH 0/2] PCI/AER: Consistently use _OSC to determine who owns
 AER
To: Keith Busch <keith.busch@intel.com>
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From: Sinan Kaya <okaya@kernel.org>
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Date: Tue, 20 Nov 2018 17:28:49 -0500
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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.