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SubjectRe: using IS_ENABLED(CONFIG_xyz) effectively
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Hi Geert,

On Monday 16 November 2015 01:58 PM, Geert Uytterhoeven wrote:
> Hi Vineet,
>
> On Mon, Nov 16, 2015 at 9:00 AM, Vineet Gupta
> <Vineet.Gupta1@synopsys.com> wrote:
>> I've been using IS_ENABLED for some time and once in a while run into an issue
>> which prevents seamless use. Hence posing this question to experts in the area.
>>
>> C macro processor evaluates the ensuing control block even if IS_ENABLED evaluates
>> to false. This requires dummy #defines or worse still removing usage of IS_ENABLED
>> altogether.
>>
>> e.g. In example below even for ARCOMPACT builds, we need the ARCV2 specific define
>> ARCV2_IRQ_DEF_PRIO.
>>
>> void arch_cpu_idle(void)
>> {
>> if (is_isa_arcompact()) { <---- IS_ENABLED(CONFIG_ISA_ARCOMPACT)
>> __asm__("sleep 0x3");
>> } else {
>> const int arg = 0x10 | ARCV2_IRQ_DEF_PRIO;
>> __asm__("sleep 0x10");
>> }
>> }
>>
>> One could argue that the interface needs to be cleanly defined to not have such
>> specific #defines in common code in first place. However sometime that becomes
>> just too tedious.
>>
>> Is there a way to get around by this ?
> Use #ifdef CONFIG_...?
>
> The advantage of IS_ENABLED() over #ifdef is that it allows compile-testing of
> the disabled code path. Of course it should only be compiled if it makes
> sense. And that's exactly what you're running into.

And I thought it was to de-uglify the code with same semantics - which doesn't
seem to be the case !
Oh well !

Thx,
-Vineet



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