linux-kernel - Re: [2/3] soc: samsung: Do not build ARMv7 PMU drivers on ARMv8

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Date:   Tue, 14 Mar 2017 20:00:09 +0530
From:   Alim Akhtar <alim.akhtar@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Kukjin Kim <kgene@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Arnd Bergmann <arnd@...db.de>,
        Kevin Hilman <khilman@...libre.com>,
        Olof Johansson <olof@...om.net>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [2/3] soc: samsung: Do not build ARMv7 PMU drivers on ARMv8



On 03/14/2017 02:44 PM, Krzysztof Kozlowski wrote:
> On Tue, Mar 14, 2017 at 10:40 AM, Alim Akhtar <alim.akhtar@...sung.com> wrote:
>>
>>
>> On 03/14/2017 01:32 PM, Krzysztof Kozlowski wrote:
>>> On Tue, Mar 14, 2017 at 9:51 AM, Alim Akhtar <alim.akhtar@...sung.com> wrote:
>>>> Hi Krzysztof,
>>>>
>>>> On 03/12/2017 03:08 AM, Krzysztof Kozlowski wrote:
>>>>> The Exynos Power Management Unit (PMU) drivers contain quite large
>>>>> static arrays of register values necessary for given Exynos SoC to enter
>>>>> low power mode.  All this data is useless for ARMv8 SoC like
>>>>> Exynos5433, because the image will not be shared between ARMv7 and
>>>>> ARMv8.
>>>>>
>>>>> Add additional Kconfig symbol for selecting the SoC-specific driver
>>>>> addons thus skipping the useless data in the final image (this is
>>>>> similar approach to chosen for Exynos clock controller drivers):
>>>>>  - exynos-pmu driver will be compiled on both architectures ARMv7
>>>>>    and ARMv8,
>>>>>  - additional driver_data for ARMv7 SoCs will not be built on ARMv8
>>>>>    and a macro will return NULL for them in of_device_id - this should
>>>>>    be safe as these compatibles cannot match on ARMv7 and driver
>>>>>    anyway handles NULL driver_data,
>>>>>  - on ARMv8 compile only exynos-pmu driver which exposes the
>>>>>    syscon-regmap for PMU address space.
>>>>>
>>>>> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
>>>>> ---
>>>>>  drivers/soc/samsung/Kconfig      |  8 +++++++-
>>>>>  drivers/soc/samsung/Makefile     |  4 +++-
>>>>>  drivers/soc/samsung/exynos-pmu.c | 22 ++++++++++++++++------
>>>>>  drivers/soc/samsung/exynos-pmu.h |  3 +++
>>>>>  4 files changed, 29 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/drivers/soc/samsung/Kconfig b/drivers/soc/samsung/Kconfig
>>>>> index 245533907d1b..8b25bd55e648 100644
>>>>> --- a/drivers/soc/samsung/Kconfig
>>>>> +++ b/drivers/soc/samsung/Kconfig
>>>>> @@ -8,7 +8,13 @@ if SOC_SAMSUNG
>>>>>
>>>>>  config EXYNOS_PMU
>>>>>       bool "Exynos PMU controller driver" if COMPILE_TEST
>>>>> -     depends on (ARM && ARCH_EXYNOS) || ((ARM || ARM64) && COMPILE_TEST)
>>>>> +     depends on ARCH_EXYNOS || ((ARM || ARM64) && COMPILE_TEST)
>>>>> +     select EXYNOS_PMU_ARM_DRIVERS if ARM && ARCH_EXYNOS
>>>>> +
>>>>
>>>> In general this patch look ok, but I was think we should make these
>>>> configs configurable via _menuconfig_. Currently these are visible only
>>>> if COMPILE_TEST is enabled.
>>>> Recently I was working on adding PMU support for Exynos7 and I face
>>>> issues when I want to disable this option and re-enable it for testing
>>>> purpose.
>>>
>>> These drivers are not available in menuconfig on purpose - these are
>>> essential parts of SoC. Without them usually something will not work
>>> so user should not be able to disable them. For all of such drivers,
>>> we use the SELECT from mach approach.
>>>
>> Well, what you are saying is very subjective. In past I have face issues
>> where to isolate or narrow down some issue, we do need to play with PMU
>> and power domains. So, having a configurable option won't hurt here.
>> Anyway if you (or anyone else) strongly feel we should be following
>> "SELECT from MACH approach" then lets follow it.
>
> For ARMv7, in the past you could not do this. It behaved (almost)
> always the same as it is now. The PMU driver was being compiled in if
> ARCH_EXYNOS is selected.
>
> On ARMv8 - Exynos7 - there was no PMU driver so indeed this behavior
> changes. However PMU driver now is necessary for pinctrl (and actually
> for some others referring by syscon) so really you cannot disable it
> and expect things to work. Menuconfig serves such purpose - user
> (distro config developer) can choose what he wants but he wants to
> boot the kernel. People in general and people setting up configs for
> distro usually do not know all the subtle SoC submodule relations for
> all of the SoCs. That is our responsibility to provide them something
> which is usable.
>
> On the other hand, for debugging we always had to change some things.
> That's debugging.
>
Ok, got it.
Feel free to add
Reviewed-by: Alim Akhtar <alim.akhtar@...sung.com>

> Best regards,
> Krzysztof
>
>
>