[PATCH V2] powerpc/powernv: Add a kmsg_dumper that flushes console output on panic

[Stewart Smith]

Russell Currey <ruscur at russell.cc> writes:
> On Fri, 2015-11-27 at 16:40 +1100, Stewart Smith wrote:
>> Russell Currey <ruscur at russell.cc> writes:
>> > On BMC machines, console output is controlled by the OPAL firmware and is
>> > only flushed when its pollers are called.  When the kernel is in a panic
>> > state, it no longer calls these pollers and thus console output does not
>> > completely flush, causing some output from the panic to be lost.
>> > 
>> > This patch adds a new kmsg_dumper which gets called at panic time to ensure
>> > panic output is not lost.  It accomplishes this by calling
>> > OPAL_CONSOLE_FLUSH
>> > in the OPAL API, and if that is not available, the pollers are called
>> > enough
>> > times to (hopefully) completely flush the buffer.
>> 
>> You may want to add to commit message that this depends on:
>> https://patchwork.ozlabs.org/patch/547379/
>> 
> It doesn't *depend* on it, it's just preferred.  It still works with older
> Skiboot versions.  I will mention it in the actual commit message for the
> next revision, though.

More meaning that it depends on that patch being merged before, say the
PCI hotplug patches, which add a *different* OPAL call at the same ID -
and that it depends on *this* patch with *this* API rather than a
modified one being merged.

Otherwise, if, say, I merged some other new OPAL call into skiboot
first, this patch would likely cause all sorts of trouble.

It's also a handy hint to Michael to ensure the skiboot side of things
is merged and okay before merging kernel things in.