linux-kernel - Re: [PATCH] ARM: dts: TI: Enable __symbols_

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Date:   Wed, 16 Aug 2017 15:57:21 -0700
From:   Frank Rowand <frowand.list@...il.com>
To:     Tom Rini <trini@...sulko.com>, devicetree@...r.kernel.org
Cc:     Tero Kristo <t-kristo@...com>, Nishanth Menon <nm@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Sekhar Nori <nsekhar@...com>,
        Jason Kridner <jkridner@...gleboard.org>,
        Drew Fustini <drew@...gleboard.org>,
        Robert Nelson <robertcnelson@...il.com>,
        Lokesh Vutla <lokeshvutla@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: TI: Enable __symbols__ in dtb files for some
 platforms

On 08/16/17 15:33, Frank Rowand wrote:
> On 08/16/17 14:59, Tom Rini wrote:
>> Build the dtb file for these platfroms with __symbol__ information
>> included.  This will reduce the size of the dtb (and resident memory
> 
> typo: reduce the size should be increase the size
> 
> 
>> usage) in exchange for allowing more types of overlays to be applied to
>> the dtb file prior to passing it to Linux and additional functionality
>> within the kernel when OF_OVERLAY is enabled.
>>
>> Cc: Jason Kridner <jkridner@...gleboard.org>
>> Cc: Drew Fustini <drew@...gleboard.org>
>> Cc: Robert Nelson <robertcnelson@...il.com>
>> Cc: Lokesh Vutla <lokeshvutla@...com>
>> Cc: Frank Rowand <frowand.list@...il.com>
>> Cc: Rob Herring <robh+dt@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Russell King <linux@...linux.org.uk>
>> Cc: devicetree@...r.kernel.org
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Tom Rini <trini@...sulko.com>
>> ---
>> This patch takes the path that Rob encouraged in my previous patch of
>> enabling __symbols__ in some platforms now (that can use it) and see if
>> a critical mass evolves that pushes towards -@ being default for all
>> dtbs.  I would suggest that the dra76 series be respun to include a hunk
>> like this at least as well, and if there's another Beagle X15 patch,
>> that too.  Russell, per some of our conversations, something like would
>> also be needed as part of using overlays to solve some of the problems
>> with Hummingboard, etc.
>> ---
>>  arch/arm/boot/dts/Makefile | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/Makefile b/arch/arm/boot/dts/Makefile
>> index 4b17f35dc9a7..6f98422ca00e 100644
>> --- a/arch/arm/boot/dts/Makefile
>> +++ b/arch/arm/boot/dts/Makefile
>> @@ -1063,3 +1063,17 @@ dtb-$(CONFIG_OF_ALL_DTBS) := $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dts
>>  
>>  always		:= $(dtb-y)
>>  clean-files	:= *.dtb
>> +
>> +# enable creation of __symbols__ node
>> +DTC_FLAGS_am335x-bone += -@
>> +DTC_FLAGS_am335x-boneblack += -@
>> +DTC_FLAGS_am335x-boneblack-wireless += -@
>> +DTC_FLAGS_am335x-boneblue += -@
>> +DTC_FLAGS_am335x-bonegreen += -@
>> +DTC_FLAGS_am335x-bonegreen-wireless += -@
>> +DTC_FLAGS_am57xx-beagle-x15 += -@
>> +DTC_FLAGS_am57xx-beagle-x15-revb1 += -@
>> +DTC_FLAGS_dra7-evm += -@
>> +DTC_FLAGS_dra72-evm += -@
>> +DTC_FLAGS_dra72-evm-revc += -@
>> +DTC_FLAGS_dra71-evm += -@
>>
> 
> I would prefer that instead of "-@", a configurable value be used.

I stated that poorly.  It was intended conceptually, not literally.

One possible concrete implementation would be to use something other
than DTC_FLAGS, for example DTC_FLAGS_EXTRA, then have the build
system choose whether to fold DTC_FLAGS_EXTRA into DTC_FLAGS, based
on some sort of configurable value.


> The current form of the patch imposes the extra overhead even
> for those who do not want to use any overlay.
> 
> Using a kernel CONFIG_ value for the "configurable value" is not
> desired because it adds a kernel configuration dependency to what
> is contained in a dtb.  I do not know if we can find another
> better way to make this configurable.  AMaybe Rob's suggestion
> of a shell variable used in the make command.
>