[U-Boot] [PATCH RESEND 2/2] cmd: fdt: add fdt overlay application subcommand

[Simon Glass]

Hi Maxime,

On 10 May 2016 at 05:45, Maxime Ripard <maxime.ripard at free-electrons.com> wrote:
> Hi Simon,
>
> I'm finally taking the time to address the reviews that have been made
> here.
>
> On Sat, Apr 09, 2016 at 12:40:14PM -0600, Simon Glass wrote:
>> Hi Maxime,
>>
>> On 4 April 2016 at 12:25, Maxime Ripard
>> <maxime.ripard at free-electrons.com> wrote:
>> > The device tree overlays are a good way to deal with user-modifyable
>> > boards or boards with some kind of an expansion mechanism where we can
>> > easily plug new board in (like the BBB or the raspberry pi).
>> >
>> > However, so far, the usual mechanism to deal with it was to have in Linux
>> > some driver detecting the expansion boards plugged in and then request
>> > these overlays using the firmware interface.
>> >
>> > That works in most cases, but in some cases, you might want to have the
>> > overlays applied before the userspace comes in. Either because the new
>> > board requires some kind of an early initialization, or because your root
>> > filesystem is accessed through that expansion board.
>> >
>> > The easiest solution in such a case is to simply have the component before
>> > Linux applying that overlay, removing all these drawbacks.
>> >
>> > Signed-off-by: Maxime Ripard <maxime.ripard at free-electrons.com>
>> > ---
>> >  cmd/Makefile          |   2 +-
>> >  cmd/fdt.c             |  19 +++
>> >  cmd/fdt_overlay.c     | 464 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> >  include/fdt_support.h |   2 +-
>> >  4 files changed, 485 insertions(+), 2 deletions(-)
>> >  create mode 100644 cmd/fdt_overlay.c
>>
>> I'm happy to take this into the U-Boot tree while you try to get it
>> applied upstream, but please confirm that you will do this and by
>> when. I suggest you sent an email referring to this patch.
>>
>> Also fdt_overlay.c should go in lib/libfdt/. If this functionality is
>> rejected for libfdt (as was fdtgrep) then we'll move it to lib/.
>
> I'm definitely ok to send it to libfdt if that's what you meant by
> upstream. I'll push it at the same time I'm pushing the next version
> of these patches, just to make sure we progress as fast as we can on
> this.

OK great.

>
>> Finally, please take a look at adding a test for this, with some
>> sample files. See test/py.
>
> However, that will be a bit difficult. In order to be used, the DT
> overlays require the overlay support in dtc, which is still not
> included upstream. So the majority of the users of U-Boot won't have
> that support, meaning that these tests will likely fail for them (even
> though the code might be correct), resulting in a lot of false
> negative.
>
> How do you want me to proceed?

Well I suppose you can write the test, but comment it out for now. We
can still try it with the out-of-tree dtc.

>
> Thanks!
> Maxime
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com

Regards,
Simon