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    SubjectRe: [RFC] asm-generic/pci_iomap.h: make custom PCI BAR requirements explicit
    On Sat, Aug 29, 2015 at 08:25:05AM -0700, Christoph Hellwig wrote:
    > On Fri, Aug 28, 2015 at 05:17:27PM -0700, Luis R. Rodriguez wrote:
    > > From: "Luis R. Rodriguez" <mcgrof@suse.com>
    > >
    > > The S390 architecture requires a custom pci_iomap() implementation
    > > as the asm-generic implementation assumes there are disjunctions
    > > between PCI BARs, and on S390 PCI BAR are not disjunctive, S390 requires
    > > the bar parameter in order to find the corresponding device and create
    > > the mapping cookie.
    > >
    > > This clash with the asm-generic pci_iomap() implementation is implicit,
    > > there are no current semantics to make this incompatability explicit.
    > > Make the S390 PCI BAR non-disjunction incompatibility explicit, and
    > > also pave the way for alternative incompatibilities to be defined.
    > >
    > > While at it, as with the ioremap*() variants, since we have no clear
    > > semantics yet well defined provide a solution for them that returns
    > > NULL. This allows architectures to move forward by defining pci_ioremap*()
    > > variants without requiring immediate changes to all architectures. Each
    > > architecture then can implement their own solution as needed and
    > > when they get to it.
    >
    > Now that you have the config symbol available why not move the S390
    > implementation to generic code based on that can kill of
    > asm/pci_iomap.h? Seems like we're really not dealing with something
    > inherent to the architecture, but two possible implementations based
    > on architecture constraints.

    That would be the other approach to take too, but perhaps that can wait
    until yet another architecture with similar requirement pops up.

    Luis


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