Re: Does dwc/pci-layerscape.c support AER?

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Jul 16, 2025 at 05:22:58PM -0400, Frank Li wrote:
> On Wed, Jul 16, 2025 at 03:42:07PM -0500, Bjorn Helgaas wrote:
> > On Wed, Jul 16, 2025 at 10:25:57AM -0700, Brian Norris wrote:
> > > On Wed, Jul 16, 2025 at 09:35:38PM +0530, Manivannan Sadhasivam wrote:
> > > > On Wed, Jul 16, 2025 at 08:20:38AM GMT, Brian Norris wrote:
> > > > > On Wed, Jul 16, 2025 at 12:47:10PM +0530, Manivannan Sadhasivam wrote:
> > > > > > On Wed, Jul 02, 2025 at 04:44:48PM GMT, Brian Norris wrote:
> > > > > > > On Wed, Jul 02, 2025 at 07:09:42PM -0400, Frank Li wrote:
> > > > > > > OTOH, I do also believe there are SoCs where DWC PCIe is
> > > > > > > available, but there is no external MSI controller, and so
> > > > > > > that same problem still may exist. I may even have such SoCs
> > > > > > > available...
> > > > > >
> > > > > > Yes, pretty much all Qcom SoCs without GIC-v3 ITS suffer from
> > > > > > this limitation.  And the same should be true for other
> > > > > > vendors also.
> > > > > >
> > > > > > Interestingly, the Qcom SoCs route the AER/PME via 'global'
> > > > > > SPI interrupt, which is only handled by the controller driver.
> > > > > > This is similar to the 'aer' SPI interrupt in layerscape
> > > > > > platforms.
> > > > >
> > > > > Yeah, I have some SoCs like this as well. But I also believe
> > > > > that I have INTx available, and that even when MSI doesn't work
> > > > > for AER/PME, INTx might.
> > > > >
> > > > > Do Qcom SoCs route INTx?
> > > >
> > > > Yes, they do. But currently, we can only use it by booting with
> > > > pcie_pme=nomsi cmdline parameter.
> >
> > Ugh.  I think these controllers might be out of spec (or maybe we're
> > not configuring MSI/MSI-X correctly for them).  Per PCIe r7.0, sec
> > 6.1.4.3:
> >
> >   While enabled for MSI or MSI-X operation, a Function is prohibited
> >   from using INTx interrupts (if implemented) to request service (MSI,
> >   MSI-X, and INTx are mutually exclusive).
> >
> > If the controller advertises MSI or MSI-X, I think we will enable it
> > and expect AER, PME, hotplug, etc. to use it.
> 
> I think it is controller implement problem, which route AER irq to
> INTx or other irq line in SOC. Consider many users have similar
> issues, can you add workaround or quirk for this type
> implementation.

I think the spec allows the AER interrupt to be routed to INTx, but
only if the Root Port doesn't advertise MSI or MSI-X support or the OS
decides not to enable MSI/MSI-X.

Since there's no generic way to say "MSI/MSI-X works on this Root
Port, but only for certain interrupts, not including AER," there's no
way for Linux to figure out that it shouldn't enable MSI/MSI-X.

*Somebody* can add some kind of quirk for this; not me because I don't
have the hardware.  It needs to be generic so the same solution works
for all these devices.

Bjorn