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Message-id: <1405509550.7368.0.camel@AMDC1943>
Subject: Re: [RESEND PATCH v2] ARM: exynos4: hotplug: Fix CPU idle clock down
 after CPU off
From: Krzysztof Kozlowski <k.kozlowski@samsung.com>
To: Tomasz Figa <t.figa@samsung.com>
Cc: Russell King <linux@arm.linux.org.uk>, Kukjin Kim <kgene.kim@samsung.com>,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Date: Wed, 16 Jul 2014 13:19:10 +0200
In-reply-to: <53C65890.8000500@samsung.com>
References: <1405499003-9975-1-git-send-email-k.kozlowski@samsung.com>
 <53C65890.8000500@samsung.com>
Sender: linux-kernel-owner@vger.kernel.org


On śro, 2014-07-16 at 12:48 +0200, Tomasz Figa wrote:
> Hi Krzysztof,
> 
> Please see my comment below.
> 
> On 16.07.2014 10:23, Krzysztof Kozlowski wrote:
> > On Exynos4 USE_DELAYED_RESET_ASSERTION must be set in
> > ARM_COREx_OPTION register during CPU power down. This is the proper way
> > of powering down CPU on Exynos4.
> > 
> > Additionally on Exynos4212 without this the CPU clock down feature won't
> > work after powering down some CPU and the online CPUs will work at full
> > frequency chosen by CPUfreq governor.
> > 
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
> 
> [snip]
> 
> > @@ -36,6 +36,14 @@ static inline void cpu_leave_lowpower(void)
> >  	  : "=&r" (v)
> >  	  : "Ir" (CR_C), "Ir" (0x40)
> >  	  : "cc");
> > +
> > +	if (soc_is_exynos4()) {
> > +		unsigned int tmp;
> > +
> > +		tmp = __raw_readl(EXYNOS_ARM_CORE_OPTION(core_id));
> > +		tmp &= ~(S5P_USE_DELAYED_RESET_ASSERTION);
> > +		__raw_writel(tmp, EXYNOS_ARM_CORE_OPTION(core_id));
> > +	}
> 
> This code is executed only if the CPU doesn't manage to power off before
> already receiving a wake-up event. Otherwise the context is lost after
> wfi(), as the core power is being cut down.
> 
> The normal wake-up path goes through platsmp's exynos_boot_secondary()
> and I believe that setting of S5P_USE_DELAYED_RESET_ASSERTION should be
> taken care there as well.

You're right. Thanks for pointing this, I'll fix it.

Best regards,
Krzysztof
> 
> Best regards,
> Tomasz

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