linux-kernel - Re: [PATCH v12 3/5] dt, numa: Add NUMA dt binding implementation.

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Date:	Mon, 29 Feb 2016 14:56:55 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Robert Richter <rric@...nel.org>
CC:	David Daney <ddaney.cavm@...il.com>,
	Will Deacon <will.deacon@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	<devicetree@...r.kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	<linux-efi@...r.kernel.org>,
	Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>,
	Robert Richter <rrichter@...ium.com>,
	<linux-kernel@...r.kernel.org>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH v12 3/5] dt, numa: Add NUMA dt binding implementation.

On 02/29/2016 11:45 AM, Robert Richter wrote:
> On 29.02.16 10:13:48, David Daney wrote:
>> On 02/29/2016 09:29 AM, Robert Richter wrote:
>>> On 22.02.16 17:58:21, David Daney wrote:
>>>> From: Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>
>>>>
>>>> ADD device tree node parsing for NUMA topology using device
>>>> "numa-node-id" property distance-map.
>>>>
>>>> Reviewed-by: Robert Richter <rrichter@...ium.com>
>>>> Signed-off-by: Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>
>>>> Signed-off-by: David Daney <david.daney@...ium.com>
>>>> ---
>>>>   drivers/of/Kconfig   |   3 +
>>>>   drivers/of/Makefile  |   1 +
>>>>   drivers/of/of_numa.c | 211 +++++++++++++++++++++++++++++++++++++++++++++++++++
>>>>   include/linux/of.h   |   9 +++
>>>>   4 files changed, 224 insertions(+)
>>>>   create mode 100644 drivers/of/of_numa.c
>>>>
>>>> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
>>>> index e2a4841..b3bec3a 100644
>>>> --- a/drivers/of/Kconfig
>>>> +++ b/drivers/of/Kconfig
>>>> @@ -112,4 +112,7 @@ config OF_OVERLAY
>>>>   	  While this option is selected automatically when needed, you can
>>>>   	  enable it manually to improve device tree unit test coverage.
>>>>
>>>> +config OF_NUMA
>>>
>>> In arch/arm64/Kconfig you now need to:
>>>
>>> 	select OF_NUMA if NUMA && OF
>>>
>>> This should depend here on OF and NUMA and enabled in that case. Why
>>> moving that to arch code?
>>
>> The dependency on of_numa.o is in the architecture specific code, so that is
>> where the Kconfig select should be too.
>
> If you grep for select in Kconfig files you will see that dependency
> checkers in the form of select ... if ... are very rare.

You are right...

$ find . -name Kconfig | xargs grep -e 'select.*if' | wc -l
1513
$ find . -name Kconfig | xargs grep -e 'select' | wc -l
14179

The 'if' variety is encountered in fewer than 11% of the cases.

That said, I am not sure if this type of statistic should be used to 
evaluate code "goodness".

[...]
>
> But to avoid arch configs in generic Kconfigs, define HAVE_OF_NUMA,
> add it as dependency to OF_NUMA and select it in arch/arm64/Kconfig.
> OF_NUMA is then enabled with defbool y if all requirements are met.
>

Really, what we want is NEEDS_OF_NUMA.  That is exactly what "select 
OF_NUMA" means.

There is no need to build a Rube Goldberg device out of these Kconfig 
things.  The "select OF_NUMA if NUMA && OF" is concise, allowed by the 
Kconfig system and exactly expresses when the file should be compiled.

Unless there are other objections, I am going to use the the Kconfig 
changes in the v12 form.

David.