Re: [PATCH v2] PCI/portdrv: Do not require an interrupt for all AER capable ports

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Dec 07, 2022 at 04:35:37PM -0600, Bjorn Helgaas wrote:
> Hi Mika,
> 
> On Wed, Dec 07, 2022 at 10:41:05AM +0200, Mika Westerberg wrote:
> > Only Root Ports and Event Collectors use MSI for AER. PCIe Switch ports
> > or endpoints on the other hand only send messages (that get collected by
> > the former). For this reason do not require PCIe switch ports and
> > endpoints to use interrupt if they support AER.
> > 
> > This allows portdrv to attach PCIe switch ports of Intel DG1 and DG2
> > discrete graphics cards. These do not declare MSI or legacy interrupts.
> 
> Help me understand more about this situation.  I guess we want portdrv
> to attach not to a GPU itself, but to a switch port on the card that
> *leads* to the GPU?

Yes correct.

> >From the patch, it looks like the only PCIe port service this switch
> port advertises is AER (not PME, DPC, hotplug, etc), and it doesn't
> have MSI or MSI-X.

Correct.

> So aerdriver should be able to register for PCIE_PORT_SERVICE_AER, but
> aer_probe() ignores everything except Root Ports and RCECs.  What's
> the benefit then?  I must be missing something.

The portdrv is needed for power management and everything else PCI even
if there is no actual "service" attached.