I like devicetree but I dislike the way it removes the compiler's ability
to remove dead code because the compiler can't know what is in the runtime
devicetree.

One common pattern is checking if a node is compatible with some compatible
string that should never happen on the target machine. i.e checking for
something that only exists on a very specific PPC platform on ARM etc.

For weird people like me that want to run Linux on FPGA softcores, processors
from 1979 etc it is better to have the most minimal kernel config possible and
for the compiler to strip out as much unneeded code and data as possible.

The following is my quick hack to add a way to hint to the compiler whether
a specific compatible check is even possible or not so it can remove deadcode
and then an example usecase.

I think this is cleaner than #ifdef..#endif all over the place but maybe
someone has a nicer way to do it.

Daniel Palmer (2):
  of: Add a variant of of_device_is_compatible() that can be build time
    culled
  gpiolib: of: Remove a bunch of compatible checks for spi controllers
    you don't have

 drivers/gpio/gpiolib-of.c | 6 +++---
 include/linux/of.h        | 2 ++
 2 files changed, 5 insertions(+), 3 deletions(-)

-- 
2.51.0

On Wed, Jan 7, 2026 at 4:07 AM Daniel Palmer <daniel@thingy.jp> wrote:
>
> I like devicetree but I dislike the way it removes the compiler's ability
> to remove dead code because the compiler can't know what is in the runtime
> devicetree.
>
> One common pattern is checking if a node is compatible with some compatible
> string that should never happen on the target machine. i.e checking for
> something that only exists on a very specific PPC platform on ARM etc.
>
> For weird people like me that want to run Linux on FPGA softcores, processors
> from 1979 etc it is better to have the most minimal kernel config possible and
> for the compiler to strip out as much unneeded code and data as possible.
>
> The following is my quick hack to add a way to hint to the compiler whether
> a specific compatible check is even possible or not so it can remove deadcode
> and then an example usecase.
>
> I think this is cleaner than #ifdef..#endif all over the place but maybe
> someone has a nicer way to do it.
>
> Daniel Palmer (2):
>   of: Add a variant of of_device_is_compatible() that can be build time
>     culled
>   gpiolib: of: Remove a bunch of compatible checks for spi controllers
>     you don't have
>
>  drivers/gpio/gpiolib-of.c | 6 +++---
>  include/linux/of.h        | 2 ++
>  2 files changed, 5 insertions(+), 3 deletions(-)
>
> --
> 2.51.0
>

That is an awesome idea, let's hear what Rob says but for GPIO I'll be
happy to take it.

Bart