Queries: Using ifdef CONFIG condition in dts files

[Pintu Agarwal <pintu.ping@gmail.com>]

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Hi,

I have a generic question regarding conditional compilation options in
dts/dtsi files.
Our Kernel version is: 4.14
Let's say I have a Kernel config such as CONFIG_XYZ.
This driver uses a CMA reserved memory and its node is defined in a
mysoc.dtsi file.
Like:
#if defined(CONFIG_XYZ)
&reserved_mem {
        xyz_region: xyz_region {
                compatible = "shared-dma-pool";
                reusable;
                size = <0x600000>;
        };
};
#endif

The problem is as follows:
a) The same kernel/dts source is shared across 2 product versions.
b) In one product we need to enable this CONFIG_XYZ but in another product
we need to disable it.
c) When we disable the CONFIG we wanted this dts node also to be disabled
together.
d) When we add "#if defined(CONFIG_XYZ)" check in the dtsi file, it works
if the CONFIG is disabled, but it does not work if CONFIG is enabled (node
is not getting created).
e) This mysoc.dtsi file is getting included in many other dts files, so we
cannot add a compilation check in Makefile. We will end up renaming many
files just to protect this one change.

Is there any other better way to handle this situation ?

I see that in latest kernel we have a conditional compilation added like
this:
#ifdef SOC_HAS_USB2_CH2
<https://elixir.bootlin.com/linux/latest/D/ident/SOC_HAS_USB2_CH2>
https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/renesas/salvator-common.dtsi#L1028


But the same is not recognized by the device tree compiler when using
kernel CONFIG_ check.

Is it the device-tree compiler issue which got fixed in the latest version ?
Or, is it because Kernel config cannot be shared with device-tree ?

Please let us know if there is any other opinion.


Thank you.

Regards,
Pintu

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