[TRIVIAL] of: per-file dtc preprocessor flags

As of today we are able to pass custom flags to dtc compiler but not
to dtc preprocessor.
This ability is required for including some board-specific header files.
It allows us to pass defined constants to dts without their duplication
in several places.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
---
 scripts/Makefile.lib | 2 ++
 1 file changed, 2 insertions(+)

On Sat, Jul 20, 2019 at 4:28 AM Eugeniy Paltsev
<Eugeniy.Paltsev@synopsys.com> wrote:
>
> As of today we are able to pass custom flags to dtc compiler but not
> to dtc preprocessor.
> This ability is required for including some board-specific header files.
> It allows us to pass defined constants to dts without their duplication
> in several places.

How to use this option in a useful way?

I see a bunch of defined constants under include/dt-bindings/.

If you are talking about code duplication across architectures,
you can include arm dtsi from arm64 dts, or vice versa.
This was made possible by the symbolic links
in scripts/dtc/include-prefixes/.

Could you please elaborate your issues if you cannot solve them
by the current strategy?



> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> ---
>  scripts/Makefile.lib | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index f1f38c8cdc74..f2595a608dce 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -166,6 +166,8 @@ dtc_cpp_flags  = -Wp,-MD,$(depfile).pre.tmp -nostdinc                    \
>                  $(addprefix -I,$(DTC_INCLUDE))                          \
>                  -undef -D__DTS__
>
> +dtc_cpp_flags  += $(DTC_CPP_FLAGS_$(basetarget))
> +
>  # Useful for describing the dependency of composite objects
>  # Usage:
>  #   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
> --
> 2.21.0
>

Hi Masahiro,

On Sat, 2019-07-20 at 11:40 +0900, Masahiro Yamada wrote:
> On Sat, Jul 20, 2019 at 4:28 AM Eugeniy Paltsev
> <Eugeniy.Paltsev@synopsys.com> wrote:
> > As of today we are able to pass custom flags to dtc compiler but not
> > to dtc preprocessor.
> > This ability is required for including some board-specific header files.
> > It allows us to pass defined constants to dts without their duplication
> > in several places.
> 
> How to use this option in a useful way?
> 
> I see a bunch of defined constants under include/dt-bindings/.
> 
> If you are talking about code duplication across architectures,
> you can include arm dtsi from arm64 dts, or vice versa.
> This was made possible by the symbolic links
> in scripts/dtc/include-prefixes/.
> 
> Could you please elaborate your issues if you cannot solve them
> by the current strategy?
> 

Here is the example:

We have several FPGA-based boards (haps_hs, haps_hs_idu,...) which are involved
in SW and HW automated verification. For some tests we randomize physical memory
location so we patch 'CONFIG_LINUX_RAM_BASE' kconfig variable and 'memory' node in
device tree. We want to keep number of patches as less as possible (to avoid
conflicts on their applying) so we want to avoid duplication and pass
'CONFIG_LINUX_RAM_BASE' directly to dts by including it from
'include/generated/autoconf.h':

----------------------------->8------------------------------------
memory {
	device_type = "memory";
-		/* CONFIG_LINUX_RAM_BASE needs to match low mem start */
-               reg = <0x80000000 0x20000000>;  /* 512 */
+               reg = <CONFIG_LINUX_RAM_BASE 0x20000000>;      /* 512 */
};
----------------------------->8------------------------------------

This patch allows us to extend the search path of include files to
include 'include/generated/autoconf.h'.

> 
> > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> > ---
> >  scripts/Makefile.lib | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index f1f38c8cdc74..f2595a608dce 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -166,6 +166,8 @@ dtc_cpp_flags  = -Wp,-MD,$(depfile).pre.tmp -nostdinc                    \
> >                  $(addprefix -I,$(DTC_INCLUDE))                          \
> >                  -undef -D__DTS__
> > 
> > +dtc_cpp_flags  += $(DTC_CPP_FLAGS_$(basetarget))
> > +
> >  # Useful for describing the dependency of composite objects
> >  # Usage:
> >  #   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
> > --
> > 2.21.0
> > 
> 
>

On Sun, Jul 21, 2019 at 12:38 AM Eugeniy Paltsev
<Eugeniy.Paltsev@synopsys.com> wrote:
>
> Hi Masahiro,
>
> On Sat, 2019-07-20 at 11:40 +0900, Masahiro Yamada wrote:
> > On Sat, Jul 20, 2019 at 4:28 AM Eugeniy Paltsev
> > <Eugeniy.Paltsev@synopsys.com> wrote:
> > > As of today we are able to pass custom flags to dtc compiler but not
> > > to dtc preprocessor.
> > > This ability is required for including some board-specific header files.
> > > It allows us to pass defined constants to dts without their duplication
> > > in several places.
> >
> > How to use this option in a useful way?
> >
> > I see a bunch of defined constants under include/dt-bindings/.
> >
> > If you are talking about code duplication across architectures,
> > you can include arm dtsi from arm64 dts, or vice versa.
> > This was made possible by the symbolic links
> > in scripts/dtc/include-prefixes/.
> >
> > Could you please elaborate your issues if you cannot solve them
> > by the current strategy?
> >
>
> Here is the example:
>
> We have several FPGA-based boards (haps_hs, haps_hs_idu,...) which are involved
> in SW and HW automated verification. For some tests we randomize physical memory
> location so we patch 'CONFIG_LINUX_RAM_BASE' kconfig variable and 'memory' node in
> device tree. We want to keep number of patches as less as possible (to avoid
> conflicts on their applying) so we want to avoid duplication and pass
> 'CONFIG_LINUX_RAM_BASE' directly to dts by including it from
> 'include/generated/autoconf.h':
>
> ----------------------------->8------------------------------------
> memory {
>         device_type = "memory";
> -               /* CONFIG_LINUX_RAM_BASE needs to match low mem start */
> -               reg = <0x80000000 0x20000000>;  /* 512 */
> +               reg = <CONFIG_LINUX_RAM_BASE 0x20000000>;      /* 512 */



So, we need the kernel configuration to build DT?

I am scared with this idea.

I believe DT files should be able to be compiled
irrespective of the .config because they are
re-used for other projects.

devicetree-rebasing is a subset of the kernel tree
that collects DT.

If you upstream that patch, this will be broken, at least.

git://git.kernel.org/pub/scm/linux/kernel/git/devicetree/devicetree-rebasing.git