[PATCHv2] ARM: EXYNOS: reset Little cores when cpu is up

[javier@osg.samsung.com (Javier Martinez Canillas)]

Hello Krzysztof,

On 09/02/2015 02:39 AM, Krzysztof Kozlowski wrote:
> On 02.09.2015 09:32, Javier Martinez Canillas wrote:
>> Hello Krzysztof,
>>
>> On 09/02/2015 02:15 AM, Krzysztof Kozlowski wrote:
>>> On 01.09.2015 23:17, Chanho Park wrote:
>>>> The cpu booting of exynos5422 has been still broken since we discussed
>>>> it in last year[1]. This patch is inspired from Odroid XU3
>>>> code (Actually, it was from samsung exynos vendor kernel)[2]. This weird
>>>> reset code was founded exynos5420 octa cores series SoCs and only
>>>> required for the first boot core is the Little core (Cortex A7).
>>>> Some of the exynos5420 boards and all of the exynos5422 boards will require
>>>> this code.
>>>>
>>>> There is two ways to check the little core is the first cpu. One is
>>>> checking GPG2CON[1] GPIO value and the other is checking the cluster
>>>> number of the first cpu. I selected the latter because it's more easier
>>>> than the former.
>>>>
>>>> [1]:http://lists.infradead.org/pipermail/linux-arm-kernel/2015-June/350632.html
>>>> [2]:https://patchwork.kernel.org/patch/6782891/
>>>>
>>>> Cc: Kevin Hilman <khilman@kernel.org>
>>>> Cc: Javier Martinez Canillas <javier@osg.samsung.com>
>>>> Cc: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>>>> Tested-by: Kevin Hilman <khilman@linaro.org>
>>>> Signed-off-by: Chanho Park <parkch98@gmail.com>
>>>> ---
>>>> Changes from v1:
>>>>  .kfc to Little (Cortex A7) and eagle to big (Cortex A15)
>>>>  .append comments about waiting SPARE2 register
>>>>
>>>> Changes since RFC:
>>>>  .drop checking soc_is_exynos5800 to extend this codes to
>>>> exynos5420/5422 boards.
>>>>  .kfc cores will be reset only if the cpu0 is kfc core.
>>>>  .Rebase top of the kukjin's for-next branch
>>>>
>>>>  arch/arm/mach-exynos/mcpm-exynos.c | 25 ++++++++++++++++++++++++-
>>>>  arch/arm/mach-exynos/regs-pmu.h    |  6 ++++++
>>>>  2 files changed, 30 insertions(+), 1 deletion(-)
>>>
>>> Thanks for updating the patch. Remaining minor nit about comment style
>>> (/* on first line) can be fixed while applying.
>>>
>>> The patch works good, after disabling bL switcher I have 8 cores running:
>>>
>>> Tested on Odroid XU4:
>>> Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>>> Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>>>
>>> It's 4.3 merge window so the patch will go probably to v4.4.
>>>
>>
>> Isn't this material for the v4.3 -rc cycle since it's fixing a bug
>> (CPUs not booting)? So I don't think that's necessary to wait for v4.4.
> 
> It is a bug fix but:
> 1. Not a fix for regression introduced in current merge window,

I thought the -rc cycle was for stabilization and fix not only regressions
introduced during the merge window but also long standing issues.

> 2. There may be more subtle issues like the one mentioned below, not
> found yet (probably no one tested it with all possible configurations),
>

Right, this is indeed a better reason to wait for v4.4.
 
> so I don't think rushing with the patch to mainline is good idea.
>

Yes, agreed.
 
> However your comment reminds me about stable. This actually looks like a
> candidate for stable.
> 
>>
>> But I was expecting another re-spin as from Abhilash's latest comments [0],
>> it seems the same workaround is needed in arch/arm/mach-exynos/platsmp.c
>> to avoid the CPU's not booting issue when CCI is disabled in DT and the
>> MCPM backend is bypassed.
>>
>> Although I guess that could be also made as a follow up patch.
> 
> Chanho patch fixes only MCPM path. Regular path (platsmp, firmware) is
> not affected so I would expect a following patch.
>

Ok, hopefully the non MCPM path can also be fixed before v4.4.
 
> Best regards,
> Krzysztof
> 
>>

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America