[PATCH v3 2/2] asm-generic: Add new pci.h and use it

[Arnd Bergmann]

On Fri, Jul 22, 2022 at 6:36 PM Rob Herring <robh at kernel.org> wrote:
> On Fri, Jul 22, 2022 at 9:27 AM Palmer Dabbelt <palmer at dabbelt.com> wrote:
>
> From fu740:
>                        ranges = <0x81000000  0x0 0x60080000  0x0
> 0x60080000 0x0 0x10000>,      /* I/O */
...
> So again, how does one get a 0 address handed out when that's not even
> a valid region according to DT? Is there some legacy stuff that
> ignores the bridge windows?

The PCI-side port number 0x60080000 gets turned into Linux I/O resource 0,
which I think is what __pci_assign_resource operates on.

The other question is why the platform would want to configure the
PCI bus to have a PCI I/O space window of size 0x10000 at the address
it's mapped into, rather than putting it at address zero. Is this a hardware
bug, a bootloader bug, or just badly set up in the DT?

Putting the PCI address of the I/O space window at port 0 is usually
better because it works with PCI devices and drivers that assume that
port numbers are below 0xfffff, and makes the PCI port number match
the Linux port number.

         Arnd