linux-kernel - Re: [PATCH v2 1/3] devicetree: bindings: Document qcom,msm-id and qcom,board-id

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Date:	Tue, 10 Mar 2015 18:01:36 -0400
From:	Rob Clark <robdclark@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Kumar Gala <galak@...eaurora.org>, Olof Johansson <olof@...om.net>,
	Kevin Hilman <khilman@...nel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arm@...nel.org" <arm@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Heiko Stübner <heiko@...ech.de>
Subject: Re: [PATCH v2 1/3] devicetree: bindings: Document qcom,msm-id and qcom,board-id

On Tue, Mar 10, 2015 at 3:52 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 10 March 2015 13:10:08 Kumar Gala wrote:
>> >>>>>>>>> The top level qcom,msm-id and qcom,board-id are utilized by bootloaders
>> >>>>>>>>>> on Qualcomm MSM platforms to determine which device tree should be
>> >>>>>>>>>> utilized and passed to the kernel.
>> >>>>>>>>>>
>> >>>>>>>>>> Cc: <devicetree@...r.kernel.org>
>> >>>>>>>>>> Signed-off-by: Kumar Gala <galak@...eaurora.org>
>> >>>>>>>>>
>> >>>>>>>>> Is this the special magic that allows qcom bootloaders to take a kernel
>> >>>>>>>>> plus multiple DTBs and figure out which DTB to pass?
>> >>>>>>>>>
>> >>>>>>>>> Kevin
>> >>>>>>>>
>> >>>>>>>> yes
>> >>>>>>>
>> >>>>>>> That's a bummer.
>> >>>>>>>
>> >>>>>>> Luckily, the solution for upstream is still quite simple: Provide only
>> >>>>>>> one devicetree, and it'll be used, right?
>> >>>>>>
>> >>>>>> We can provide only one, we still need the IDs in the DT.
>> >>>>>
>> >>>>> How are the DTS provided? Concatenated with the kernel, or in a
>> >>>>> wrapped data format? Or in a separate partition from the kernel?
>> >>>>
>> >>>> Its a wrapped data format that is than concatenated with the kernel if I remember correctly.
>> >>>
>> >>> Then you should be able to create a tool that can write this concatenated
>> >>> format and insert these properties from a table that matches the boot
>> >>> loader, right?
>> >>>
>> >>>      Arnd
>> >>
>> >> Are you suggesting the tool insert the properties in the DT?  I’m not sure I understand what the point of doing that would be.
>> >
>> > To insert platform-local properties that mean nothing outside of the
>> > firmware packaging of the device trees, which is the case here?
>> >
>> > I think the idea of having the installer script inserting them is
>> > quite reasonable in this case.
>> >
>> >
>> > -Olof
>>
>> These values are static, so not sure what the point of having the installer script do that?
>>
>
> It combines two hacks to work around a nonstandard boot loader.
> Once the bootloader is fixed, you can stop using that script.
>

still sounds like an extra hurdle for distro's..  can't you just add
the extra entry in the dts files w/ a comment about workaround for
bootloader (and then possibly *not* document the property)?

BR,
-R

>         Arnd
> --
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