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

[Simon Glass]

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.

Regards,
SImon