linux-kernel - Re: [PATCH 1/2] clk: samsung: Don't build ARMv8 clock drivers on ARMv7

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Date:	Thu, 19 Nov 2015 13:51:30 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Tomasz Figa <tomasz.figa@...il.com>
Cc:	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, linux-clk@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Kukjin Kim <kgene@...nel.org>, Olof Johansson <olof@...om.net>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Kevin Hilman <khilman@...aro.org>,
	Pankaj Dubey <pankaj.dubey@...sung.com>
Subject: Re: [PATCH 1/2] clk: samsung: Don't build ARMv8 clock drivers on ARMv7

On 19.11.2015 13:18, Tomasz Figa wrote:
> Hi Krzysztof,
> 
> Good idea, just a couple of nits inline. Other than that:
> 
> Acked-by: Tomasz Figa <tomasz.figa@...il.com>
> 
> 2015-11-16 10:36 GMT+09:00 Krzysztof Kozlowski <k.kozlowski@...sung.com>:
>> Currently the Exynos5433 (ARMv8 SoC) clock driver depends on ARCH_EXYNOS
>> so it is built also on ARMv7. This does not bring any kind of benefit.
>> There won't be a single kernel image for ARMv7 and ARMv8 SoCs (like
>> multi_v7 for ARMv7).
>>
>> Instead build clock drivers only for respective SoC's architecture.
>>
>> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
>> ---
>>  drivers/clk/samsung/Kconfig  | 13 +++++++++++++
>>  drivers/clk/samsung/Makefile |  4 ++--
>>  2 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/clk/samsung/Kconfig b/drivers/clk/samsung/Kconfig
>> index 84196ecdaa12..5f138fc4d84d 100644
>> --- a/drivers/clk/samsung/Kconfig
>> +++ b/drivers/clk/samsung/Kconfig
>> @@ -2,6 +2,7 @@ config COMMON_CLK_SAMSUNG
>>         bool
>>         select COMMON_CLK
>>
>> +# ARMv7 SoCs:
> 
> nit: I'm not aware of any recent upgrade of the S3C24xx line-up to
> ARMv7 cores. ;) I'd suggest "32-bit ARM SoCs" or just "ARM SoCs"...

okay

> 
>>  config S3C2410_COMMON_CLK
>>         bool
>>         select COMMON_CLK_SAMSUNG
>> @@ -24,3 +25,15 @@ config S3C2443_COMMON_CLK
>>         bool
>>         select COMMON_CLK_SAMSUNG
>>
>> +# ARMv8 SoCs:
> 
> and then here "64-bit ARM SoCs" or "ARM64 SoCs", whichever you prefer.
> I'd lean towards simple "ARM" and "ARM64".

ARM64 sounds good.

> 
>> +config EXYNOS5433_COMMON_CLK
>> +       bool
>> +       depends on ARM64 || COMPILE_TEST
>> +       default ARCH_EXYNOS
> 
> nit: bool and default can be combined into def_bool ARCH_EXYNOS
> 

Right.

>> +       select COMMON_CLK_SAMSUNG
>> +
>> +config EXYNOS7_COMMON_CLK
>> +       bool
>> +       depends on ARM64 || COMPILE_TEST
>> +       default ARCH_EXYNOS
> 
> nit: See above.
> 
> However, I don't think we can disable compilation of particular 64-bit
> SoCs, so maybe there isn't much sense in splitting their clock drivers
> into separate symbols?

To me it does not really matter. Indeed as you said one cannot disable
building of one particular Exynos SoCs.

However we could still want not build some parts of such SoCs (like
clock, pinctrl etc). I don't see much benefit for such case except when
someone would like to drastically reduce the size of kernel image (for
whatever reasons he has.).

On the other hand having separate symbols causes duplication and
obfuscates a little the Kconfig/Makefile. I like keeping things simple
so one symbol for all ARM64 Exynos clocks sounds good.

Sylwester preferred current approach. You and Pankaj seem to prefer one
symbol-way.

Should we make a voting? :)

Best regards,
Krzysztof
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