Re: [PATCH 7/7] ARM: EXYNOS: Remove code for restart and poweroff for exynos SoCs

From: Javier Martinez Canillas <javier@osg.samsung.com>
To: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Alim Akhtar <alim.akhtar@samsung.com>,
	linux-samsung-soc@vger.kernel.org, kgene@kernel.org,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 7/7] ARM: EXYNOS: Remove code for restart and poweroff for exynos SoCs
Date: Mon, 19 Oct 2015 16:07:46 +0200	[thread overview]
Message-ID: <5624F932.7030001@osg.samsung.com> (raw)
In-Reply-To: <CAJKOXPcvKeDNwof5eyD5XjzUiZrHoyShD8gOPGo7uUxEyypQbw@mail.gmail.com>

Hello Krzysztof,

On 10/19/2015 03:28 PM, Krzysztof Kozlowski wrote:
> 2015-10-19 18:56 GMT+09:00 Javier Martinez Canillas <javier@osg.samsung.com>:
>> Hello,
>>
>> On 10/19/2015 09:00 AM, Krzysztof Kozlowski wrote:
>>> On 19.10.2015 15:03, Alim Akhtar wrote:
>>>> Now we can use the generic syscon-{reboot/poweroff} drivers,
>>>> so we don't need special handling for reboot/poweroff in
>>>> exynos pmu driver. This patch remove the same.
>>>>
>>>> Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
>>>> ---
>>>>  arch/arm/mach-exynos/pmu.c |   43 -------------------------------------------
>>>>  1 file changed, 43 deletions(-)
>>>
>>> I think that removal of this stuff will effectively remove the
>>> restart/poweroff handlers from:
>>> 1. Other defconfigs, like multi_v7
>>> 2. Custom configs.
>>>
>>
>> This will also break old DTBs that don't have a "syscon-poweroff" device
>> node that contains the necessary PMU regmap, offset and mask information.
> 
> I am not sure whether this is ABI break issue. There was no compatible
> mentioning that "reset works" which now would be replaced. The
> existing PMU compatible (like samsung,exynos4412-pmu) does not mention
> "reset" as a feature coming with this compatible.
> 
> So no ABI break.
> 
> 

I deliberately didn't use the "DT ABI break" expression since as you said is
not part of the documented DT bindings. But what I said is that this change
will break old DTBs with newer kernels since reboot and power off will stop
working after $SUBJECT.

I'm not a particular fan of the stable DT idea since in practice it seems to
do more harm than good but since that was decided, the expectation for users
is that booting a new kernel with an old DT should not cause any regression.

So I think that at least a comment in the commit message is needed so if
there are people really using old DTs with newer kernels on Exynos boards,
they can know that the commit causes such an issue instead of having to
figure it out themselves.

>>
>>> Previously this code was always compiled in for ARCH_EXYNOS. Now it is
>>> not so I am thinking about selecting necessary drivers from main exynos
>>> Kconfig symbol. That could be tricky though, because "select" should be
>>> used only for non-visible symbols.
>>>
>>> Any ideas how to solve that?
>>>
>>
>> Is true that select should only be used for non-visible symbols but there
>> are others user visible symbols that are selected by ARCH_EXYNOS such as
>> EXYNOS_THERMAL. So I think selecting the regmap syscon reset stuff there
>> is a sensible option.
> 
> Selecting from defconfig is not sufficient... since I do not have
> other idea than selecting then ovak, but Alim please check it whether
> it does not create circular dependencies on various configs.
>

Agreed, Kconfig circular dependencies is the reason why select is avoided.
Fortunately now the 0-day bot analyzes even posted patches so it's possible
that such an issue could be found even before these patches are merged.

> Best regards,
> Krzysztof
>

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