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    SubjectRe: [PATCH-RFC 1/2] tile: don't panic on iomap
    On Tue, Nov 29, 2011 at 10:54 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
    > I think panic on iomap is there just for debugging.
    > If we return NULL instead, the generic pci_iomap will
    > DTRT so we don't need to roll our own.

    Just to be explicit about what "doing the right thing" means, here's
    what I think is changing (I think the new behavior is OK, but it *is*
    different):

    Old behavior: Caller calls pci_iomap(), which panics in ioport_map().

    New behavior: Caller calls pci_iomap(), ioport_map() returns NULL,
    pci_iomap() returns NULL (failure), caller may check for failure. If
    caller does not check for failure and passes the NULL to
    ioread()/iowrite(), we WARN in bad_io_access().

    >  static inline void __iomem *ioport_map(unsigned long port, unsigned int len)
    >  {
    > -       return (void __iomem *) ioport_panic();
    > +       pr_info("Trying to map an IO resource - it does not exit on tile.\n");
    > +       return NULL;

    s/exit/exist/

    Since we only expect to see this message during debugging, maybe it
    could be more informative, e.g., use dump_stack() to identify the
    offending driver? I don't think either the "Trying to map" message or
    the "Bad IO access" message is enough to actually make progress in
    debugging.

    Bjorn
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