linux-kernel - Re: local bus enumeration beyond a PCI device

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Message-ID: <ZiYZK9Jb-4qiGQ7C@surfacebook.localdomain>
Date: Mon, 22 Apr 2024 11:00:43 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
	"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>,
	Herve Codina <herve.codina@...tlin.com>
Subject: Re: local bus enumeration beyond a PCI device

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