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

Stefan Roese
2021-12-14T12:48:44Z

On 12/14/21 13:45, Marek Behún wrote:
> 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.

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