[U-Boot] Makefile: Only build dtc if needed

[Tom Rini]

On Sun, Apr 26, 2020 at 06:34:48PM -0600, Simon Glass wrote:
> Hi Tom,
> 
> On Sat, 26 Jan 2019 at 20:51, Tom Rini <trini at konsulko.com> wrote:
> >
> > On Tue, Nov 13, 2018 at 03:43:07PM -0700, Simon Glass wrote:
> >
> > > At present U-Boot always builds dtc if CONFIG_OF_CONTROL is defined. This
> > > is wasteful when the system already has a suitable version available.
> > >
> > > Update the Makefile logic to build dtc only if the version available is
> > > too old.
> > >
> > > This saves about 3 seconds of CPU time on a clean build for me.
> > >
> > > Signed-off-by: Simon Glass <sjg at chromium.org>
> > > Reviewed-by: Marek Vasut <marek.vasut at gmail.com>
> >
> > In the case of new enough host dtc this then fails on sandbox_spl,
> > chromebook_minnie and others where we need to build
> > spl/dts/dt-platdata.c with a python import error over lacking _libfdt.
> 
> I'm not sure if it has been long enough, but have the packages been
> updated to include pylibfdt?
> 
> I'm sending a new version of this patch that checks for that.

I honestly don't know how far behind distributions lag here and then in
turn how old something is before we say "sorry, you can't build there
easily".

-- 
Tom
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