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

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Message-Id: <7DA73171-01A5-4158-9A69-015B62D2D7E8@codeaurora.org>
Date:	Tue, 10 Mar 2015 14:57:47 -0500
From:	Kumar Gala <galak@...eaurora.org>
To:	Arnd Bergmann <arnd@...db.de>
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 Mar 10, 2015, at 2:52 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.
> 
> 	Arnd

I feel as if I’m missing something here.  If we just have the properties in the .dts files I don’t need to change anything ever, no script, no worries about working with old or new boot loaders, etc.

- k

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

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