On Sun, Apr 19, 2020 at 4:11 AM Nicolas Pitre <nico@xxxxxxxxxxx> wrote:
>
> On Sun, 19 Apr 2020, Masahiro Yamada wrote:
>
> > (FOO || !FOO) is difficult to understand, but
> > the behavior of "uses FOO" is as difficult to grasp.
>
> Can't this be expressed as the following instead:
>
> depends on FOO if FOO
>
> That would be a little clearer.
>
>
> Nicolas
'depends on' does not take the 'if <expr>'
'depends on A if B' is the syntax sugar of
'depends on (A || !B), right ?
I do not know how clearer it would make things.
depends on (m || FOO != m)
is another equivalent, but we are always
talking about a matter of expression.
How important is it to stick to
depends on (FOO || !FOO)
or its equivalents?
If a driver wants to use the feature FOO
in most usecases, 'depends on FOO' is sensible.
If FOO is just optional, you can get rid of the dependency,
and IS_REACHABLE() will do logically correct things.
I do not think IS_REACHABLE() is too bad,
but if it is confusing, we can add one more
option to make it explicit.
config DRIVER_X
tristate "driver x"
config DRIVER_X_USES_FOO
bool "use FOO from driver X"
depends on DRIVER_X
depends on DRIVER_X <= FOO
help
DRIVER_X works without FOO, but
Using FOO will provide better usability.
Say Y if you want to make driver X use FOO.
Of course,
if (IS_ENABLED(CONFIG_DRIVER_X_USES_FOO))
foo_init();
works like
if (IS_REACHABLE(CONFIG_FOO))
foo_init();
At lease, it will eliminate a question like
"I loaded the module FOO, I swear.
But my built-in driver X still would not use FOO, why?"
--
Best Regards
Masahiro Yamada
