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

[Stefan Roese]

On 12/14/21 13:45, Marek Behún wrote:

On Tue, 14 Dec 2021 12:12:34 +0100
Pali Rohár <p...@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 <p...@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.

Yes, the #ifdef's really should be avoided if possible. So *if* your
patch above does not generate any build issues, then I don't see any
problems to include it. I personally don't think that we need to support
-O0 builds.

Thanks,
Stefan