Re: Queries: Using ifdef CONFIG condition in dts files

[T.Michael Turney <quic_mturney@quicinc.com>]

Kernel developers correct me where I go astray, but this seems like the 
CONFIG_XYZ value is not available in this file.  This would explain why 
the disable case works.

At top of dtsi file are you #include <config.h> or whatever the correct 
syntax is to see the CONFIG values?
Cheers,
T.mike

On 5/26/2022 1:46 AM, Pintu Agarwal wrote:
> 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/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