On Tue, Jul 17, 2012 at 10:25 PM, Ram Pai <linuxram@xxxxxxxxxx> wrote: > 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@xxxxxxxxxxxxxxxxxxx> 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. Of course, you're absolutely right; I had this backwards. In pbus_size_io/mem(), we do "b_res = find_free_bus_resource()", so b_res is a bus resource that matches the desired type (IO/MEM). This resource represents an aperture of the upstream bridge leading to the bus. I was thinking that b_res->start would contain address information that the arch could use to decide alignment. But at this point, in pbus_size_io/mem(), we set "b_res->start = min_align", so obviously b_res contains no information about the window base that will eventually be assigned. I think b_res is basically the *container* into which we'll eventually put the P2P aperture start/end, but here, we're using that container to hold the information about the size and alignment we need for that aperture. The fact that we deal with alignment in pbus_size_mem() and again in __pci_assign_resource() (via pcibios_align_resource) is confusing to me -- I don't have a clear idea of what sorts of alignment are done in each place. Could this powerpc alignment be done in pcibios_align_resource()? We do have the actual proposed address there, as well as the pci_dev. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
