lkml.org 
[lkml]   [2011]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
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 <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):

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");
?

--
MST
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-11-30 08:05    [from the cache]
©2003-2011 Jasper Spaans