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

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Date:   Wed, 23 Oct 2019 20:45:00 -0700
From:   Olof Johansson <olof@...om.net>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Keith Busch <keith.busch@...el.com>, linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI/DPC: Add pcie_ports=dpc-native parameter to bring
 back old behavior

On Wed, Oct 23, 2019 at 7:37 PM Keith Busch <kbusch@...nel.org> 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.
> >
> > To make DPC still work on said platforms the same way they did before,
> > add a "pcie_ports=dpc-native" kernel parameter that can be passed in
> > if needed, while keeping defaults unchanged.
>
> If platform firmware wants to handle AER events, but the kernel enables
> the DPC capability, the ports will be trapping events that firmware is
> expecting to handle. Not that that's a bad thing: firmware is generally
> worse at handling these errors.

Right, and in particular (and what I'm looking for here): It brings
back the older behavior that some platforms rely on. :-/

> > +/*
> > + * If the user specified "pcie_ports=dpc-native", use the PCIe services
> > + * for DPC, but cuse platform defaults for the others.
>
> s/cuse/use

Thanks

> > @@ -1534,9 +1534,11 @@ static inline int pci_irqd_intx_xlate(struct irq_domain *d,
> >  #ifdef CONFIG_PCIEPORTBUS
> >  extern bool pcie_ports_disabled;
> >  extern bool pcie_ports_native;
> > +extern bool pcie_ports_dpc_native;
> >  #else
> >  #define pcie_ports_disabled  true
> >  #define pcie_ports_native    false
> > +#define pcie_ports_dpc_native        false
> >  #endif
>
> You do not have any references to pcie_ports_dpc_native outside of files that
> require CONFIG_PCIEPORTBUS, so no need to define a default.

If these are the only comments, maybe Bjorn can fixup when applying.
Bjorn; let me know if you prefer that or if you want a fresh version.
Either is fine with me.


-Olof