Re: [PATCH V7 1/3] kbuild: Add generic rule to apply fdtoverlay

On Fri, Feb 12, 2021 at 5:05 AM Rob Herring [off-list ref] wrote:

On Thu, Feb 11, 2021 at 12:28 PM Masahiro Yamada [off-list ref] wrote:

quoted

On Wed, Feb 10, 2021 at 8:13 PM Viresh Kumar [off-list ref] wrote:

quoted

From: Rob Herring <robh@kernel.org>

Add a generic rule to apply fdtoverlay in Makefile.lib, so every
platform doesn't need to carry the complex rule.

The platform's Makefile only needs to have this now:

 DTC_FLAGS_foo_base += -@
 foo-dtbs := foo_base.dtb foo_overlay1.dtbo foo_overlay2.dtbo
 overlay-y := foo.dtb

Please reuse dtb-y instead of introducing the new
overlay-y syntax, that is,

foo-dtbs := foo_base.dtb foo_overlay1.dtbo foo_overlay2.dtbo
dtb-y := foo.dtb

That's what I had, but I believe Viresh changed this because we don't
want to run schema checks on foo.dtb (as foo.dts doesn't exist).
However, we should be able to filter those out using something similar
to technique used for multi-used-y and real-obj-y. We just need to
drop composite entries when creating the .dt.yaml list.

Yes, I think this will work.



BTW, I do not know how to use overlay.
Do we apply overlay in the build time?
If so, I do not know what the benefit of overlay is.
Or is this just for build testing?


I just thought this was done in the boot time,
for example, in U-Boot or something.




-- 
Best Regards
Masahiro Yamada