Re: [PATCH 1/4] ARM: exynos: Apply little core workaround only under secure firmware

From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Krzysztof Kozlowski <krzk@kernel.org>, Lukasz Luba <lukasz.luba@arm.com>
Cc: linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH 1/4] ARM: exynos: Apply little core workaround only under secure firmware
Date: Mon, 29 Jun 2020 10:54:27 +0200	[thread overview]
Message-ID: <96d7f0f2-63c0-8c8d-5a79-ba27295b389a@samsung.com> (raw)
In-Reply-To: <20200622171904.GA4174@kozik-lap>

Hi Krzysztof,

On 22.06.2020 19:19, Krzysztof Kozlowski wrote:
> On Wed, Jun 17, 2020 at 05:26:58PM +0100, Lukasz Luba wrote:
>> I've give it a try with hotplug torture tests and has only one a minor
>> comment.
>>
>> On 6/16/20 9:12 AM, Marek Szyprowski wrote:
>>> The additional soft-reset call during little core power up was needed
>>> to properly boot all cores on the Exynos5422-based boards with secure
>>> firmware (like Odroid XU3/XU4 family). This however broke big.LITTLE
>>> CPUidle driver, which worked only on boards without secure firmware
>>> (like Peach-Pit/Pi Chromebooks).
>>>
>>> Apply the workaround only when board is running under secure firmware.
>>>
>>> Fixes: 833b 5794 e330 ("ARM: EXYNOS: reset Little cores when cpu is up")
> Fix the Fixes tag (in case of resend, otherwise I'll do it).
>
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>> ---
>>>    arch/arm/mach-exynos/mcpm-exynos.c | 10 +++++++---
>>>    1 file changed, 7 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
>>> index 9a681b421ae1..cd861c57d5ad 100644
>>> --- a/arch/arm/mach-exynos/mcpm-exynos.c
>>> +++ b/arch/arm/mach-exynos/mcpm-exynos.c
>>> @@ -26,6 +26,7 @@
>>>    #define EXYNOS5420_USE_L2_COMMON_UP_STATE	BIT(30)
>>>    static void __iomem *ns_sram_base_addr __ro_after_init;
>>> +static bool secure_firmware __ro_after_init;
>>>    /*
>>>     * The common v7_exit_coherency_flush API could not be used because of the
>>> @@ -58,15 +59,16 @@ static void __iomem *ns_sram_base_addr __ro_after_init;
>>>    static int exynos_cpu_powerup(unsigned int cpu, unsigned int cluster)
>>>    {
>>>    	unsigned int cpunr = cpu + (cluster * EXYNOS5420_CPUS_PER_CLUSTER);
>>> +	bool state;
>>>    	pr_debug("%s: cpu %u cluster %u\n", __func__, cpu, cluster);
>>>    	if (cpu >= EXYNOS5420_CPUS_PER_CLUSTER ||
>>>    		cluster >= EXYNOS5420_NR_CLUSTERS)
>>>    		return -EINVAL;
>>> -	if (!exynos_cpu_power_state(cpunr)) {
>>> -		exynos_cpu_power_up(cpunr);
>>> -
>>> +	state = exynos_cpu_power_state(cpunr);
>>> +	exynos_cpu_power_up(cpunr);
>> I can see that you have moved this call up, probably to avoid more
>> 'if-else' stuff. I just wanted to notify you that this function
>> 'exynos_cpu_powerup' is called twice when cpu is going up:
>> 1. by the already running cpu i.e. CPU0 and the 'state' is 0 for i.e.
>> CPU2
>> 2. by the newly starting cpu i.e. CPU2 by running
>> 'secondary_start_kernel' and the state is 3.
>>
>> In this scenario the 'exynos_cpu_power_up' will be called twice.
>> I have checked in hotplug that this is not causing any issues, but
>> thought maybe it's worth share it with you. Maybe you can double check
>> in TRM that this is not causing anything.
> This brings the old code, before 833b5794e33. I wonder why? I understood
> that only soft-reset should be skipped.

Because otherwise the Peach boards hangs during the cpuidle. I didn't 
analyze the code that much to judge if it is really necessary in all 
cases, I only restored what worked initially. I can add a comment about 
that to the commit log if needed.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland