Re: Question about Odroid XU4 cpuidle

From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Lukasz Luba <lukasz.luba@arm.com>, Krzysztof Kozlowski <krzk@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	"linux-samsung-soc@vger.kernel.org" 
	<linux-samsung-soc@vger.kernel.org>,
	Andrzej Hajda <a.hajda@samsung.com>,
	s.nawrocki@samsung.com
Subject: Re: Question about Odroid XU4 cpuidle
Date: Mon, 15 Jun 2020 14:45:16 +0200	[thread overview]
Message-ID: <26daae4c-684a-7319-ae6c-f3319ba0406d@samsung.com> (raw)
In-Reply-To: <8c0a8cc6-9cc0-88b5-6614-67edb903d149@arm.com>

Hi Lukasz

On 10.06.2020 16:30, Lukasz Luba wrote:
> On 6/10/20 3:09 PM, Marek Szyprowski wrote:
>> On 10.06.2020 16:02, Krzysztof Kozlowski wrote:
>>> On Wed, Jun 10, 2020 at 02:18:12PM +0100, Lukasz Luba wrote:
>>>> Hi Krzysztof, Bartek,
>>>>
>>>> I recall that you have been working on some cpuidle code for 
>>>> Exynos(4?).
>>>>
>>>> I have a question regarding CPUIdle driver for Odroid XU4.
>>>> I use the board with LISA tests for EAS, but missing at
>>>> least idle state 0 cause errors (please see the log below).
>>>>
>>>> Currently the system does not report any idle driver and the state 0
>>>> is missing in: /sys/devices/system/cpu/cpu0/cpuidle/state0/
>>> The state 0 long time ago was WFI. It was kind of meaningless so it it
>>> was dropped.
>>>
>>>> I am using driver CONFIG_ARM_BIG_LITTLE_CPUIDLE but the
>>>> boot stops silently while trying to init the cpu idle devices in 
>>>> there.
>>>> I carry on with a workaround that just removes idle state[1] and set
>>>> state_count=1 in the big and little structures.
>>> Try earlyprintk.
>>>
>>> In general, the big-little cpuidle driver should work... or rather: 
>>> long
>>> time ago it was working.  It requires proper support from early stages
>>> (BL1, secure monitor) but this should be already in standard Odroid.
>>>
>>> I just saw there:
>>>     /* Start at index 1, index 0 standard WFI */
>>> so maybe it was not updated properly to removal of WFI?
>>>
>>> I think no one uses this driver so it might be not well tested and not
>>> that useful.
>>
>> I think it never worked on Odroid XU3/XU4. Afair it was developed on
>> PeachPi Chromebook, which use different bootloader (and doesn't use
>> trustzone).
>
> That would explain the compatibility string in that driver. Good to
> know. Thank you for your response.
>
I've just digged a bit in the old kernels and indeed, the big-little 
cpuidle driver worked only on Samsung Exynos 5420/5800 Chromebooks 
(Peach Pit/Pi). The last release which worked fine (although it was 
still not enabled in the exynos_defconfig) is v4.2. Then it got broken 
by the commit 833b5794e330 ("ARM: EXYNOS: reset Little cores when cpu is 
up"). It never worked on the Odroid XU3/XU4.

Do you have any plans to fix it?

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