linux-kernel - local bus enumeration beyond a PCI device

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Message-ID: <bad63409-ed2b-4cef-988b-3c143636e9fa@alliedtelesis.co.nz>
Date: Thu, 18 Apr 2024 00:24:06 +0000
From: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: local bus enumeration beyond a PCI device

Hi,

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.

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?

Thanks,
Chris