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

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Message-ID: <87mwft1j7f.fsf@approximate.cambridge.arm.com>
Date:	Thu, 10 Apr 2014 13:07:32 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Chanwoo Choi <cw00.choi@...sung.com>
Cc:	"kgene.kim\@samsung.com" <kgene.kim@...sung.com>,
	"t.figa\@samsung.com" <t.figa@...sung.com>,
	"linux-samsung-soc\@vger.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"hyunhee.kim\@samsung.com" <hyunhee.kim@...sung.com>,
	"sw0312.kim\@samsung.com" <sw0312.kim@...sung.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"yj44.cho\@samsung.com" <yj44.cho@...sung.com>,
	"inki.dae\@samsung.com" <inki.dae@...sung.com>,
	"kyungmin.park\@samsung.com" <kyungmin.park@...sung.com>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 06/27] ARM: EXYNOS:: Enter a15 lowpower mode for Exynos3250 based on Cortex-a7

On Thu, Apr 10 2014 at 11:56:33 am BST, Chanwoo Choi <cw00.choi@...sung.com> wrote:
> On 04/10/2014 06:51 PM, Marc Zyngier wrote:
>> On Thu, Apr 10 2014 at 10:28:23 am BST, Chanwoo Choi <cw00.choi@...sung.com> 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 <cw00.choi@...sung.com>
>>> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
>>> ---
>>>  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();

Yup, even better.

>> 
>>> -	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;
> 	}

Looks good.

	M.
-- 
Jazz is not dead. It just smells funny.
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