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    SubjectRe: [PATCH-RFC 1/2] tile: don't panic on iomap
    On Tue, Nov 29, 2011 at 01:04:12PM -0800, Bjorn Helgaas wrote:
    > On Tue, Nov 29, 2011 at 10:54 AM, Michael S. Tsirkin <> 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):

    I think the change is that anyone calling ioport_map *directly*
    will fail. pci_iomap callers are mostly unaffected.

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

    Not really, the old pci_iomap simply returned NULL in this case, it
    did not call 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

    As explained above, only direct callers of ioport_map get a changed
    behaviour. If we start dumping stack there we will hurt users of
    pci_iomap which used to get a graceful failure and will start getting
    scary messages. Is does not seem to be worth doing to simplify debugging, right?
    How about sticking the function name in the pr_info message?
    A simple grep for ioport_map will then get you the culprit ...
    Like this:
    +       pr_info("ioport_map: mapping IO resources is unsupported on tile.\n");

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      Last update: 2011-11-30 08:05    [W:0.025 / U:7.016 seconds]
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