Re: local bus enumeration beyond a PCI device

Andy Shevchenko
2024-04-22T08:00:46Z

Thu, Apr 18, 2024 at 01:45:31PM -0500, Bjorn Helgaas kirjoitti:
> On Thu, Apr 18, 2024 at 12:24:06AM +0000, Chris Packham wrote:

> > We've got a custom x86_64 based design that is using an ASIX9100 to
> > provide a PCI to local bus bridge. Attached to that local bus is an FPGA
> > which mostly provides some GPIOs accessed via registers on the local
> > bus. Right now we've got a custom driver that bundles everything
> > together so effectively we've got a PCI device that provides GPIOs.
>
> What's the local bus? The ASIX9100 (for which Google doesn't find any
> details) would have a PCI interface on the primary (upstream) side.
> What's the local bus on the secondary (downstream) side? Below you
> mention "PCI bridge", which normally means both the primary and
> secondary sides are PCI buses.
>
> If the local bus is not PCI, I guess the ASIX9100 would look to the OS
> like an endpoint, i.e., PCI_HEADER_TYPE_NORMAL, and the ASIX9100
> driver would handle any "bridge" functionality completely internally?
>
> Maybe Herve's work at
> https://lore.kernel.org/r/20240325153919.199337-1-herve.codina@bootlin.com
> would be relevant?

+1 here. Thought the same when seeing the original message from Chris.

> > But as things can change based on the FPGA program I'd like some
> > flexibility to treat it separately from the PCI bridge. So really I'd
> > like to have a PCI device driver for the ASIX9100 that provides a local
> > bus controller and a (platform?) driver for the FPGA that provides the
> > GPIOs where I can have different compatibles for the different
> > implementations.
> >
> > Then in the ACPI overlay I'd have something like
> >
> >     Scope (\_SB.PCI0.D0B0)
> >     {
> >         Device (ASIX)
> >         {
> >             Name (_ADR, 0x0000)
> >
> >             Device (FPGA)
> >             {
> >                         Name (_HID, "PRP0001")
> >                         Name (_DSD, Package ()
> >                         {
> > ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> >                                     Package ()
> >                                     {
> >                                                 Package () {
> > "compatible", "my-platform-driver-for-fpga" },
> >                                     }
> >                         })
> >             }
> >         }
> >     }
> >
> >    Scope(\_SB)
> >    {
> >         Device(OTHR)
> >         {
> >             GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
> > "\\_SB.PCI0.D0B0.ASIX.FPGA",) { 0 }
> >         }
> >    }
> >
> > Is it even possible to register a host controller for another platform bus?

--
With Best Regards,
Andy Shevchenko