Re: Lack of _HPX after reset, DPC

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

Hi Bjorn,

On Tue, Jul 16, 2024 at 5:45 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> I think Linux is missing some important _HPX functionality.  Per ACPI
> r6.5, sec 6.2.9,
>
>   OSPM uses the information returned by _HPX to determine how to
>   configure PCI Functions that are hot-plugged into the system, to
>   configure Functions not configured by the platform firmware during
>   initial system boot, and to configure Functions any time they lose
>   configuration space settings (e.g. OSPM issues a Secondary Bus
>   Reset/Function Level Reset or Downstream Port Containment is
>   triggered).
>
> Linux currently *does* process _HPX for hot-added devices.
>
> The spec doesn't call it out for boot-time enumeration, except for
> "Functions not configured by the platform firmware during initial
> system boot", but Linux does process _HPX for all devices enumerated
> at boot-time because it's not clear how to identify devices that
> weren't configured by firmware.
>
> But AFAICT, Linux does not do anything with _HPX in the device reset,
> AER, or DPC flows.  I don't have any problem reports that I can say
> are caused by lack of _HPX after reset, but it seems like something we
> should fix.

The consumer grade devices I checked don't have _HPX in the ACPI ASL.
So I can't really delve into it any further.

Kai-Heng

>
> If we could find a system with _HPX that does something interesting,
> we might be able to demonstrate a defect by looking at a device before
> and after a reset.
>
> Bjorn