[PATCH] ARM: S5PV310: Optimize interrupt source searching code

[Michał Nazarewicz]

On Tue, 28 Sep 2010 14:45:59 +0200, Sergei Shtylyov <sshtylyov at mvista.com> wrote:

> Hello.
>
> On 28-09-2010 5:31, Kukjin Kim wrote:
>
>> From: Changhwan Youn<chaos.youn at samsung.com>
>
>> It is reported by Junseok Jung that using clz instruction is
>> better instead of using for-loop to find the interrupt source.
>> This patch modifies interrupt source searching code using __fls().
>> The __fls() is implemented using clz instruction.
>
>> Suggested-by: Junseok Jung<jundols.jung at samsung.com>
>> Signed-off-by: Changhwan Youn<chaos.youn at samsung.com>
>> Signed-off-by: Kukjin Kim<kgene.kim at samsung.com>
>> ---
>>   arch/arm/mach-s5pv310/irq-combiner.c |    6 +-----
>>   1 files changed, 1 insertions(+), 5 deletions(-)
>
>> diff --git a/arch/arm/mach-s5pv310/irq-combiner.c b/arch/arm/mach-s5pv310/irq-combiner.c
>> index 0f70521..39e3647 100644
>> --- a/arch/arm/mach-s5pv310/irq-combiner.c
>> +++ b/arch/arm/mach-s5pv310/irq-combiner.c
>> @@ -66,11 +66,7 @@ static void combiner_handle_cascade_irq(unsigned int irq, struct irq_desc *desc)
>>   	if (status == 0)
>>   		goto out;
>>
>> -	for (combiner_irq = 0; combiner_irq<  32; combiner_irq++) {
>> -		if (status & 0x1)
>> -			break;
>> -		status>>= 1;
>> -	}
>> +	combiner_irq = __fls(status);
>
>     But the loop finds the *first* set bit, not the last...

__ffs than?

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