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 20:52:01 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Kumar Gala <galak@...eaurora.org>
Cc:	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 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.

	Arnd
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