Hi Stephen,
On Sat, May 8, 2021 at 10:59 AM Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Masahiro,
>
> On Thu, 6 May 2021 02:45:15 +0900 Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> >
> > <linux/kconfig.h> is included from all the kernel-space source files,
> > including C, assembly, linker scripts. It is intended to contain a
> > minimal set of macros to evaluate CONFIG options.
> >
> > IF_ENABLED() is an intruder here because (x ? y : z) is C code, which
> > should not be included from assembly files or linker scripts.
>
> Except it doesn't matter unless IF_ENABLED() is used by one of those.
Yes. This is rather coding policy of <linux/kconfig.h>
> > Also, <linux/kconfig.h> is no longer self-contained because NULL is
> > defined in <linux/stddef.h>.
>
> Again, it doesn't matter unless IF_ENABLED() is used.
If you want to use IF_ENABLED(), you must understand that
it is internally using NULL and include <linux/stddef.h>.
It is the reason why we should make headers self-contained.
>
> > Move IF_ENABLED() out to <linux/kernel.h> as PTR_IF(). PTF_IF()
> > takes the general boolean expression instead of a CONFIG option
> > so that it fits better in <linux/kernel.h>.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> > ---
> >
> > Changes in v2:
> > - Keep PTF_IF macro in pinctrl-ingenic.c
> >
> > drivers/pinctrl/pinctrl-ingenic.c | 2 ++
> > include/linux/kconfig.h | 6 ------
> > include/linux/kernel.h | 2 ++
> > 3 files changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/pinctrl/pinctrl-ingenic.c b/drivers/pinctrl/pinctrl-ingenic.c
> > index 651a36b9dcc0..0ee69f8e20b2 100644
> > --- a/drivers/pinctrl/pinctrl-ingenic.c
> > +++ b/drivers/pinctrl/pinctrl-ingenic.c
> > @@ -3854,6 +3854,8 @@ static int __init ingenic_pinctrl_probe(struct platform_device *pdev)
> > return 0;
> > }
> >
> > +#define IF_ENABLED(cfg, ptr) PTR_IF(IS_ENABLED(cfg), (ptr))
> > +
> > static const struct of_device_id ingenic_pinctrl_of_match[] = {
> > {
> > .compatible = "ingenic,jz4730-pinctrl",
>
> You also need to include linux/kernel.h in
> drivers/pinctrl/pinctrl-ingenic.c (for completeness).
<linux/kernel.h> is too widely used, so some other headers
would have already included it eventually.
But, correct, it is better to include it explicitly for completeness.
>
> Also, I don't understand why the use of IF_ENABLED doesn't produce
> "defined but not used" warnings (if the function "ptr" is not marked as
> __maybe_unused) ...
The function is optimized out by the compiler, not by the pre-processor.
So, -Wunused-but-set-variable does not complain about it.
> Also, if there is only one user of IF_ENABLED (and therefore PTR_IF),
> why not just put it in that file and save me rebuilding the world again
> every day because kernel.h is changed (again). I guess that is going
> to happen just because kconfig.h is being changed and that is also
> included by everything :-(
I understand, but this is a one-time fix.
<linux/kconfig.h> is not changed so often.
I believe this will be useful for SET_SYSTEM_SLEEP_PM_OPS cleanups.
So, the macro must be placed in a public header.
> Also, is anyone else ever going to use PTR_IF() without having to also
> use IS_ENABLED()?
Yes or no. I am not sure about the future of this.
I prefer this in a more general expression,
so IS_REACHABLE or the combination of two CONFIG options
will work.
PTR_IF(IS_REACHABLE(CONFIG_FOO), ...)
PTR_IF( IS_ENABLED(CONFIG_FOO) && IS_ENABLED(CONFIG_BAR), ...)
>
> So, in case it is not obvious, I consider this patch unnecessary churn
> (as was probably the patch that introduced IF_ENABLED in the first
> place).
>
> As an aside, this should not have been added to the kbuild tree in
> linux-next until after -rc1 was released ...
Rather, I was considering sending a pull req before -rc1.
Otherwise, other drivers may start to use it.
>
> --
> Cheers,
> Stephen Rothwell
--
Best Regards
Masahiro Yamada
