Re: [PATCH] PCI: Only enable IO window if supported

[Guenter Roeck]

Bjorn,

On 06/02/2015 12:58 PM, Bjorn Helgaas wrote:
> On Tue, Jun 2, 2015 at 12:02 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
[ ... ]
> > > > I wonder if we can do the same with pci_read_bridge_mmio_pref(), and
> > > > somehow get rid of pci_bridge_check_ranges() altogether?
> > > >
> > > > I think I looked at doing that a while back, and it seems like there was
> > > > some wrinkle, but I don't remember what it was.
> >
> > After looking into this some more, I think the wrinkle may be that
> > pci_read_bridge_bases() and thus pci_read_bridge_io() isn't called
> > on probe-only systems (if PCI_PROBE_ONLY is set). A secondary
> > problem is that pci_read_bridge_io() does not enable a resource
> > if it is explicitly disabled (base > limit), but the subsequent call
> > to pci_bridge_check_ranges() unconditionally enables it.
>
> I haven't researched this, but it sounds wrong that we skip
> pci_read_bridge_bases() if PCI_PROBE_ONLY is set.  I think
> PCI_PROBE_ONLY should mean "look, but don't touch."  So I think we
> should always look at the bridge windows, and my advice is to see if
> it looks reasonable to change this aspect of PCI_PROBE_ONLY.

Looks like Lorenzo's patch is going to take care of that problem.

How about the second problem mentioned above ? One option might be to
keep pci_bridge_check_ranges() but only use it to _enable_ the various
ranges (and maybe rename it accordingly) ?

Thanks,
Guenter

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