When the EEH (enhanced i/o error handling) hardware on pSeries detects
various kinds of PCI errors, it immediately freezes and isolates the slot
of the offending PCI card.  We get to know about that by noticing that
reads from the device return all-1s, and then we have to do a firmware call
to find out whether the all-1s value was due to a slot isolation.

This patch adds a notifier so that other parts of the system (e.g.  the RPA
PCI hotplug driver) can know that a slot isolation event has occurred and
take whatever recovery action is appropriate.  The notifier is called in a
workqueue function, although the read from the device that noticed the
all-1s value may have been at interrupt level.  As a precaution, if we keep
trying to read from the device at interrupt level, and do 1000 reads
without the workqueue getting a chance to run, we panic, on the grounds
that we presumably have a badly-written driver which will spin forever in
its interrupt routine, e.g.  waiting for a bit in a device register to go
to 0.

This patch is based on an earlier patch by Linas Vepstas <linas@linas.org>.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>