Re: [PATCH v4 19/21] drivers/of: Support adding sub-tree

Hi Ben,

On May 2, 2015, at 01:57 , Benjamin Herrenschmidt =

[off-list ref] wrote:

=20
On Fri, 2015-05-01 at 13:46 -0500, Rob Herring wrote:

quoted

On Fri, May 1, 2015 at 10:22 AM, Benjamin Herrenschmidt
[off-list ref] wrote:

quoted

On Fri, 2015-05-01 at 07:54 -0500, Rob Herring wrote:
=20

quoted

The difference seems to be whether you allocate space or just point =

to

quoted

quoted

quoted

the FDT for various strings/data. Is that right?
=20

quoted

  * of_fdt_add_subtree() is the introduced API to do the work.

=20
Have you looked at overlays and if so why do they not work for your =

purposes?

quoted

quoted

quoted

=20
Why do you need to do this with the flattened tree?

=20
The basic idea I asked Gavin to implement is that since the FW needs =

to

quoted

quoted

provide a bunch of DT updates to Linux at runtime in the form of new
nodes below an existing one, rather than doing it via some =

new/custom

quoted

quoted

format, instead, have it send a bit of FDT blob to expand under an
existing node.

=20
Overlay =3D an FDT blob to graft into a live running system. Sounds =

like

quoted

the same thing.
=20

quoted

As for the details of Gavin implementation, I haven't looked at it =

in

quoted

quoted

details yet so there might be issues there, however I don't know =

what

quoted

quoted

you mean by "overlays", any pointer ?

=20
CONFIG_OF_OVERLAY
=20
=

http://events.linuxfoundation.org/sites/events/files/slides/dynamic-dt-key=
note-v3.pdf

=20
Well, that looks horrendously complicated, poorly documented and =

totally

unused in-tree outside of the unittest stuff, yay ! It has all sort of
"features" that I don't really care about.
=20

If it was easy to get stuff in, it would get more of the real-use =
drivers
in.

I still don't see what it buys me other than making my FW a lot more
complex having to generate all that additional fixup etc... crap that =

I

don't totally get yet.
=20

You don=E2=80=99t generate any additional fixups. You just compile with =
the option
that generates all the fixups for you.

What's wrong with just unflattening the nodes in place ? The DT comes
from the FW in the first place so all the phandles are already good in
the new added blob. Internally, the FW created new nodes in its =

internal

representation and flattened the subtree and sends that subtree to
Linux.
=20
I don't plan to play "revert" either, if you unplug, I do need to =

remove

what's under the slot but that's true of boot time devices, not just
"new" ones, so the overlay stuff won't do the trick and I certainly
don't want to keep track=E2=80=A6
=20

You get all of the corner cases handled for free. Perhaps it works for =
your
case too.

Perhaps you can educate me on what you need supported and we can make =
sure
it=E2=80=99s included.

Ben.
=20
=20

Regards

=E2=80=94 Pantelis