IBM 440GX, Ocotea...

Paul Mackerras paulus at
Thu Mar 25 23:12:16 EST 2004

Jaap-Jan Boor writes:

> In addition to this nice tree discussion, I've a question:
> from what 'official ppc' tree do patches eventually get into the
> official linux kernel tree(s) at
> only linuxppc-2.4? Or all?

Well, the thing to understand is that there is no automatic,
effortless way that code goes into the trees.  Every change
that goes in involves somebody putting together a patch against the
current state of the official trees, together with a
description of what is being changed and why it is being changed, and
sending that to Marcelo Tosatti, Andrew Morton or Linus Torvalds.

BitKeeper can help to some extent with this, mainly by providing a way
for us to send Marcelo/Andrew/Linus a bunch of changes in one go.  It
doesn't, however, provide any automatic way for changes to get from
the linuxppc-2.4 or linuxppc-2.5 trees into their trees.  The reason
is that with BK, if you pull the changes from one tree into another
tree, you have to take all the changes in the first tree that aren't
in the second.  You can't pick and choose which changesets get
transferred.  Therefore, we don't ask Marcelo/Andrew/Linus to pull
from linuxppc-2.[45] into their trees.  There is too much stuff in
there that isn't ready, or that I don't agree with, or that I just
don't understand.

I have taken on the role of ppc32 maintainer, part of which involves
sending changes to Marcelo/Andrew/Linus.  However, doing that involves
work on my part to identify which changes in linuxppc-2.[45] are ready
to send, which changes logically go together, and I have to be able to
explain the change.

When it comes to things like the 8xx/82xx/85xx support, I rely on the
maintainers for that area -- Tom Rini and Dan Malek -- to do that work
of identifying sets of related changes that are suitable for inclusion
in the official trees, and packaging them up with an explanation so
that they can be sent upstream.  (That can be done either with patches
or BK changesets; the amount of work required is pretty much the same
either way.)

Similarly, for the boot code I look to Tom and for the powermac
support I look to Ben Herrenschmidt.  For the 4xx stuff there isn't
really a maintainer at the moment, unfortunately, except that Matt
Porter is looking after the 44x boards.  I look after the classic
PowerPC core support -- exception handling, memory management, etc.,
and to some extent the 4xx core support, and the CHRP port.

What this boils down to is that for changes in these areas I expect
the maintainers for those areas to be packaging up the changes with
explanations, ready to go upstream.  Anyone is of course welcome to
put together a patch + explanation and propose that it go upstream.
In such cases I would ask the maintainer for that area for his
opinion, or if there isn't a maintainer, I would ask the submitter if
they will commit to maintaining that area of the code.  If they won't,
I would tend to drop the patch unless it is a simple, obviously
correct bugfix.

One problem we have at present is that there are a number of board
ports which don't appear to have a maintainer.  Sometimes there are
people using those ports but noone taking responsibility for updating
it and keeping it working as things change elsewhere in the kernel.
Having a maintainer is a prerequisite for the board port to be sent

I hope this clarifies things.  If you want the trees to
support your platform, then I suggest you put together the changes you
want to see as patches and send them to me and the maintainer for the
subarea.  Make sure that the patch comes with a good explanation of
the change, and if you think the patch should go upstream, say so.  If
possible make sure that the patch isn't too large.  If it is large,
see if you can split it up into smaller patches, each of which
contains a logically related set of changes.


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