Subject: [PATCH 06/27] ARM: EXYNOS:: Enter a15 lowpower mode for Exynos3250 based on Cortex-a7

From: [email-masked] (Chanwoo Choi)
Date: Thu, 10 Apr 2014 19:56:33 +0900

On 04/10/2014 06:51 PM, Marc Zyngier wrote:
> On Thu, Apr 10 2014 at 10:28:23 am BST, Chanwoo Choi <[email-masked]> wrote:
>> This patch decide proper lowpower mode of either a15 or a9 according to own ID
>> from Main ID register.
>>
>> Signed-off-by: Chanwoo Choi <[email-masked]>
>> Signed-off-by: Kyungmin Park <[email-masked]>
>> ---
>>  arch/arm/mach-exynos/hotplug.c | 13 ++++++++++---
>>  1 file changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm/mach-exynos/hotplug.c b/arch/arm/mach-exynos/hotplug.c
>> index 5eead53..36d3db6 100644
>> --- a/arch/arm/mach-exynos/hotplug.c
>> +++ b/arch/arm/mach-exynos/hotplug.c
>> @@ -135,13 +135,20 @@ void __ref exynos_cpu_die(unsigned int cpu)
>>  	int primary_part = 0;
>>  
>>  	/*
>> -	 * we're ready for shutdown now, so do it.
>> -	 * Exynos4 is A9 based while Exynos5 is A15; check the CPU part
>> +	 * we're ready for shutdown now, so do it. Exynos4 is A9 based
>> +	 * while Exynos5 is A15/Exynos7 is A7; check the CPU part
>>  	 * number by reading the Main ID register and then perform the
>>  	 * appropriate sequence for entering low power.
>>  	 */
>>  	asm("mrc p15, 0, %0, c0, c0, 0" : "=r"(primary_part) : : "cc");
> 
> While you're touching that code, how about using:
> 
>       primary_part = read_cpuid(CPUID_ID);

Or, 
I suggest read_cpuid_part_number() instead of assembler directly.

	primary_part = read_cpuid_part_number();

> 
>> -	if ((primary_part & 0xfff0) == 0xc0f0)
>> +
>> +	/*
>> +	 * Main ID register of Cortex series
>> +	 * - Cortex-a7  : 0x410F_C07x
>> +	 * - Cortex-a15 : 0x410F_C0Fx
>> +	 */
>> +	primary_part = primary_part & 0xfff0;
>> +	if (primary_part == 0xc0f0 || primary_part == 0xc070)
> 
> ARM_CPU_PART_CORTEX_A15, ARM_CPU_PART_CORTEX_A7

OK I'll use this defined constant as following:

	switch (primary_part)
	case ARM_CPU_PART_CORTEX_A7:
	case ARM_CPU_PART_CORTEX_A15:
		cpu_enter_lowpower_a15();
		break;
	default:
		cpu_enter_lowpower_a9();
		break;
	}

> 
>>  		cpu_enter_lowpower_a15();
>>  	else
>>  		cpu_enter_lowpower_a9();
> 

Best Regards,
Chanwoo Choi