[PATCH v3 3/3] PCI: ARM: add support for generic PCI host controller

[Will Deacon]

On Tue, Feb 18, 2014 at 08:15:12PM +0000, Arnd Bergmann wrote:
> On Tuesday 18 February 2014 18:44:20 Will Deacon wrote:
> > On Tue, Feb 18, 2014 at 06:21:42PM +0000, Jason Gunthorpe wrote:
> > > On Tue, Feb 18, 2014 at 12:20:43PM +0000, Will Deacon wrote:
> > > > +
> > > > +    // BUS_ADDRESS(3)  CPU_PHYSICAL(2)  SIZE(2)
> > > > +    ranges = <0x1000000 0x0 0x00000000  0x0 0x00000000  0x0 0x00010000>,
> > >                                            ^^^^^^^^^^^^^^
> > > 
> > > This probably shouldn't be 0 in the example, nor in your kvm tool
> > > output. For example purposes any value will do.
> > 
> > Hmm, so kvmtool actually provides a PC ioport at 0x0, which is handy since
> > there's an 8250 down there. That means we have:
> > 
> > 0x0    - 0x6200  : Weird PC stuff
> > 0x6200 - 0x10000 : PCI IO space
> > 
> > Should I just change everything to be offset by 0x6200?
> 
> Some more comments about this:
> 
> * After I looked at the kvmtool code some more, I think it would be nice to
>   actually move the I/O space window to a nonzero location, e.g. between the
>   PCI space and the AXI space. It's really confusing the way it is, and easy
>   to introduce bugs if you have any code that accidentally relies on the
>   numbers matching up. For all I can tell, kvmtool should just work fine
>   with any definition of ARM_IOPORT_AREA, as long as you apply the trivial
>   patch below.

Well, I think we need a bit more than that otherwise our I/O BARs won't be
initialised correctly.

> * pci_get_io_space_block() is a very confusing name for a function that
>   allocates a memory space block in kvmtool. It seems that KVM_IOPORT_AREA
>   is a misnomer for the same reason. Note that PowerPC sets KVM_IOPORT_AREA
>   to zero, but has the I/O space window at SPAPR_PCI_IO_WIN_ADDR, 
>   which is non-zero.

Agreed about pci_get_io_space_block being a misnomer, that's probably due
some cleanup. I don't think KVM_IOPORT_AREA is too bad though (it's zero for
PowerPC because I added it and don't have a platform to test on).

> * It's interesting that you also support I/O space access to the PCI config
>   space through PC-Style ports 0cf8-0cff. Not sure if that helps at all,
>   but it is another standard way to probe the bus that could easily be
>   implemented as an alternative to CAM and ECAM, in a generic PCI host
>   driver.

I won't add that initially, but if somebody needs it then it's easy to
extend what we currently have.

Will