Re: [PATCH] PCI/DPC: Add pcie_ports=dpc-native parameter to bring back old behavior

[Olof Johansson]

On Thu, Nov 7, 2019 at 12:02 PM Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> On 10/25/19 1:20 PM, Bjorn Helgaas wrote:
> > On Wed, Oct 23, 2019 at 12:22:05PM -0700, Olof Johansson wrote:
> >> In commit eed85ff4c0da7 ("PCI/DPC: Enable DPC only if AER is available"),
> >> the behavior was changed such that native (kernel) handling of DPC
> >> got tied to whether the kernel also handled AER. While this is what
> >> the standard recommends, there are BIOSes out there that lack the DPC
> >> handling since it was never required in the past.
> > Some systems do not grant OS control of AER via _OSC.  I guess the
> > problem is that on those systems, the OS DPC driver used to work, but
> > after eed85ff4c0da7, it does not.  Right?
>
> I need some clarification on this issue. Do you mean in these systems,
> firmware expects OS to handle DPC and AER, but it does not let OS know
> about it via _OSC ?

The OS and BIOS both assumed behavior as before eed85ff4c0da7 -- AER
handled by firmware but DPC handled by kernel.

I.e. a classic case of "Sure, the spec says this, but in reality
implementations relied on actual behavior", and someone had a
regression and need a way to restore previous behavior.


-Olof