[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 <pali at 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 at 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