BugLink: http://bugs.launchpad.net/bugs/1486180

Commit 89a51df5 ("powerpc/eeh: Fix crash in eeh_add_device_early() on Cell")
added a check on function eeh_add_device_early(): since in Cell arch eeh_ops
is NULL, that code used to crash on Cell. The commit's approach was validate
if EEH was available by checking the result of function eeh_enabled().

Since the function eeh_add_device_early() is used to perform EEH
initialization in devices added later on the system, like in hotplug/DLPAR
scenarios, we might reach a case in which no PCI devices are present on boot
and so EEH is not initialized. Then, if a device is added via DLPAR for
example, eeh_add_device_early() fails because eeh_enabled() is false.

We can hit a kernel oops on pSeries arch if eeh_add_device_early() fails:
if we have no PCI devices on machine at boot time, and then we add a PCI device
via DLPAR operation, the function query_ddw() triggers the oops on NULL pointer
dereference in the line "cfg_addr = edev->config_addr;". It happens because
config_addr in edev is NULL, since the function eeh_add_device_early() was not
completed successfully.

This patch just changes the way the arch checking is done in function
eeh_add_device_early(): we use no more eeh_enabled(), but instead we check the
running architecture by using the macro machine_is(). If we are running on
pSeries or PowerNV, the EEH mechanism can be enabled; otherwise, we bail out
the function. This way, we don't enable EEH on Cell and we don't hit the oops
on DLPAR either.

Fixes: 89a51df5 ("powerpc/eeh: Fix crash in eeh_add_device_early() on Cell")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>