Re: [PATCH u-boot-marvell v2 8/9] arm: mvebu: spl: Use IS_ENABLED() instead of #ifdef where possible

Marek Behún
2021-12-14T12:45:50Z

On Tue, 14 Dec 2021 12:12:34 +0100
Pali Rohár <pali@kernel.org> wrote:

> On Tuesday 14 December 2021 10:45:15 Marek Behún wrote:
> > On Tue, 14 Dec 2021 10:36:00 +0100
> > Pali Rohár <pali@kernel.org> wrote:
> >
> > > On Friday 26 November 2021 15:37:37 Marek Behún wrote:
> > > > @@ -340,17 +333,17 @@ void board_init_f(ulong dummy)
> > > > timer_init();
> > > >
> > > > /* Armada 375 does not support SerDes and DDR3 init yet */
> > > > -#if !defined(CONFIG_ARMADA_375)
> > > > - /* First init the serdes PHY's */
> > > > - serdes_phy_config();
> > > > -
> > > > - /* Setup DDR */
> > > > - ret = ddr3_init();
> > > > - if (ret) {
> > > > - debug("ddr3_init() failed: %d\n", ret);
> > > > - hang();
> > > > + if (!IS_ENABLED(CONFIG_ARMADA_375)) {
> > > > + /* First init the serdes PHY's */
> > > > + serdes_phy_config();
> > > > +
> > > > + /* Setup DDR */
> > > > + ret = ddr3_init();
> > > > + if (ret) {
> > > > + debug("ddr3_init() failed: %d\n", ret);
> > > > + hang();
> > > > + }
> > > > }
> > > > -#endif
> > >
> > > As written in comment above there is no SerDes and DDR3 support for
> > > Armada 375 and therefore there is no serdes_phy_config() or ddr3_init()
> > > function. So this code needs not to be compiled at all and usage of
> > > #ifdef is correct here.
> >
> > #ifdefs are almost never correct in C-files, for the parts of the code
> > they guard isn't put through syntactic analysis, and can therefore
> > contain bugs which we are not warned about.
> >
> > Using if (IS_ENABLED()) almost never producess a different binary,
> > because the code is optimized away.
> >
> > Marek
>
> There is no function serdes_phy_config() for Armada 375, so if you put
> it outside of #ifdef you will get compile error.

The function is always declared in
arch/arm/mach-mvebu/include/mach/cpu.h
regardless of architecture.

Thus an error will be raised only when linking, and the compliation was
done with -O0, which I don't think anyone does.

Anyway, if we want to support -O0, this can and should be solved via
defining serdes_phy_config() as empty static inline function in the
cpu.h header, guarded by #ifdef. In header files #ifdefs are allowed,
in this manner:
#if X
declare function
#else
define that function as empty static inline
#endif

So if you think we should support -O0, I can do this.

But the #ifdefs should really go away from real C code, that is the way
both Linux and U-Boot are trying to go for the last couple of years, if
I understand it correctly.

Marek