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

- From: Bjorn Helgaas \<bhelgaas@google.com\>
- Date: 2012-07-17 17:15:15 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2012/07/9470295
- Thread: https://ratatoskr.run/linux-pci/2012/07/9470286/t.md

```text
On Tue, Jul 17, 2012 at 4:38 AM, Benjamin Herrenschmidt
[ref] 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)
```