Re: [PATCH 05/15] pci: resource assignment based on p2p alignment

[Ram Pai <linuxram@us.ibm.com>]

On Tue, Jul 17, 2012 at 11:14:51AM -0600, Bjorn Helgaas wrote:
> On Tue, Jul 17, 2012 at 4:38 AM, Benjamin Herrenschmidt
> <benh@kernel.crashing.org> wrote:
> > On Tue, 2012-07-17 at 18:03 +0800, Ram Pai wrote:
> >>         Lets say we passed that 'type' flag to size the minimum
> >>         alignment constraints for that b_res.  And window_alignment(bus,
> >>         type) of your platform  used that 'type' information to
> >>         determine whether to use the alignment constraints of 32-bit
> >>         window or 64-bit window.
> >>
> >>         However, later when the b_res is actually allocated a resource,
> >>         the pci_assign_resource() has no idea whether to allocate 32-bit
> >>         window resource or 64-bit window resource, because the 'type'
> >>         information is not captured anywhere in b_res.
> >>
> >>         You would basically have a disconnect between what is sized and
> >>         what is allocated. Unless offcourse you pass that 'type' to
> >>         the b_res->flags, which is currently not the case.
> >
> > Right, we ideally would need the core to query the alignment once per
> > "apertures" it tries as a candidate to allocate a given resource... but
> > that's for later.
> >
> > For now we can probably live with giving out the max of the minimum
> > alignment we support for M64 and our M32 segment size.
> 
> We already know the aperture we're proposing to allocate from (the
> result of find_free_bus_resource()), don't we?  What if we passed it
> to pcibios_window_alignment() along with the struct pci_bus *, e.g.:
> 
>   resource_size_t pcibios_window_alignment(struct pci_bus *bus, struct
> resource *window)

Hmm..'struct resource *window' may not yet know which aperature it is
allocated from. Will it? We are still in the sizing process, the allocation will
be done much later.

RP