Re: [RFC] ARM/ARM64 PCI_PROBE_ONLY platforms

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Jan 29, 2016 at 05:25:38PM -0600, Bjorn Helgaas wrote:
> On Wed, Jan 20, 2016 at 06:10:03PM +0000, Lorenzo Pieralisi wrote:
> 
> > To do that, we must claim resources on PCI_PROBE_ONLY systems, but
> > I know for certain Bjorn does not like the idea (I let you trawl
> > the archives - at least he does not accept the idea of claiming
> > resources ONLY on PCI_PROBE_ONLY systems, he thinks we should
> > always claim resources regardless of that flag and fall-back to
> > reassigning them in case claiming fails. That's perfectly reasonable,
> > at least on systems with FW initializing PCI). The problem is dealing
> > with legacy, so switching to resources claiming by default is a tad
> > complicated, at least for testing (code is easy to implement).
> 
> I'd like to think of PCI_PROBE_ONLY basically as "setting
> IORESOURCE_PCI_FIXED for every BAR", i.e., we can do everything we
> normally do *except* write to the BAR (of course we have to write to
> it to size the BAR during enumeration, but we have to restore the
> original value).

I am honestly a bit confused about the distinction between
PCI_PROBE_ONLY and "IORESOURCE_PCI_FIXED for every BAR", the more
so if I read the resources assignment code, in particular:

pci_assign_resource()

in drivers/pci/setup-res.c

That function assigns the resource but does not update the BAR
if IORESOURCE_PCI_FIXED is set. I wonder why the resource is
assigned at all if IORESOURCE_PCI_FIXED is set, probably to
initialize its parent pointer and set it, still, the value in
the struct resource may differ from what's in the BAR, I am not sure
I understand why we are happy with that or I am reading code the
wrong way (does not this give a view of resource tree disconnected
from how HW is actually programmed ?)

> I don't think PCI_PROBE_ONLY should have anything to do with the
> iomem_resource and ioport_resource trees.  /proc/iomem and
> /proc/ioports should still contain every resource we know about,
> regardless of whether PCI_PROBE_ONLY is set or not.

I do not think PCI_PROBE_ONLY should have anything to do with the
resource tree either, still, if resources are not assigned, they must be
inserted in the resource tree anyway so that we are capable of enabling
the PCI devices (ie pci_enable_resources()).

Thanks,
Lorenzo