[U-Boot] [PATCH 00/19] fdt: Move to the new upstream pylibfdt library

[Tom Rini <trini@konsulko.com>]

On Tue, Apr 18, 2017 at 10:27:37AM -0600, Simon Glass wrote:
> Hi Tom,
> 
> On 18 April 2017 at 10:25, Tom Rini <trini@konsulko.com> wrote:
> >
> > On Sun, Apr 16, 2017 at 08:22:14PM -0600, Simon Glass wrote:
> >
> > > Python libfdt bindings have recently been accepted upstream. While the
> > > internals have changed a fair bit most of the API remains the same. Still,
> > > a few functions are different from how they are used in U-Boot so changes
> > > are needed to make this work.
> > >
> > > At present in U-Boot there are two libraries for accessing a device tree
> > > file:
> > >
> > > - FdtNormal which uses U-Boot's own Python bindings
> > > - FdtFallback which uses the fdtget command-line utility
> > >
> > > The latter is not a great solution: it is fairly slow since the DT is
> > > re-read for every access and it cannot provide DT offsets or packing of
> > > the DT.
> > >
> > > In addition, U-Boot now builds the libfdt module if swig is available,
> > > meaning that the fallback module is not used in that case.
> > >
> > > Finally, at some point in the future distributions may start packaging the
> > > libfdt Python module and it will be available without U-Boot needing to
> > > build it itself.
> > >
> > > Therefore it seems like a good idea to take this opportunity to drop the
> > > fallback module and just require that the Python libfdt bindings be
> > > present (at least if need by the build).
> > >
> > > The bindings are needed in two situations:
> > > - When dtoc is used to convert a device tree into C code. This is enabled
> > >     by CONFIG_SPL_OF_PLATDATA
> > > - When binman is used to produce a firmware image. This is used on all x86
> > >     and sunxi boards at present
> > >
> > > This series:
> > > - Plumbs in building the Python libfdt module to the U-Boot build system
> > > - Ensures that the module is always built if needed, print an error if
> > >     swig is not available (and thus the module cannot be built)
> > > - Allows use of a libfdt.py module already installed on the machine
> > > - Drops the FdtFallback support
> > > - Moves fdt.h and libfdt.h into lib/libfdt to aid with syncing with
> > >     upstream, building the Python bindings and to keep the code together
> > > - Merges Fdt and FdtNormal to simplify the code
> > > - Adjusts the Fdt library to work with the new libfdt module
> > > - Adds a few more tests to check access to properties in the DT
> > > - Adjusts binman and dtoc to work with the new approach
> > >
> > > It should be possible to easily sync libfdt's Python bindings with U-Boot
> > > in the future, as development there proceeds.
> >
> > While this came in late, my gut feeling is that it would be best to have
> > this change in the next release (so that various upstreams can get used
> > to the idea of basically always needing python installed to build).
> 
> I'm a little worried that it might cause problems. I made it so that
> it only *requires* python if is it actually needed, though it always
> builds libfdt.py if it can. Or perhaps that is what you are saying,
> that the only way to flush out upstream issues is to apply it?

What I'm saying is that distros (Fedora, openSUSE, OpenEmbedded) are
going to make a blanket change (if they haven't already) to say that
building U-Boot requires python to be installed (since they aren't
likely to try and optimize it on a board-by-board basis when it's "easy"
to just say it's an always dependency).  If you think there's risk with
the change itself, we can wait a release, that's fine too.  Thanks!

-- 
Tom
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