linux-kernel - Re: [PATCH v2 1/8] arm64: dts: db820c: add basic board support

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Message-ID: <20160622160452.GN1256@tuxbot>
Date:	Wed, 22 Jun 2016 09:04:52 -0700
From:	Bjorn Andersson <bjorn.andersson@...aro.org>
To:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:	Andy Gross <andy.gross@...aro.org>, devicetree@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Brown <david.brown@...aro.org>,
	Rob Herring <robh+dt@...nel.org>, linux-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/8] arm64: dts: db820c: add basic board support

On Wed 22 Jun 01:52 PDT 2016, Srinivas Kandagatla wrote:

> 
> 
> On 22/06/16 05:49, Bjorn Andersson wrote:
> >On Tue 21 Jun 10:22 PDT 2016, Srinivas Kandagatla wrote:
> >
> >[..]
> >>diff --git a/arch/arm64/boot/dts/qcom/apq8096-db820c.dts b/arch/arm64/boot/dts/qcom/apq8096-db820c.dts
> >[..]
> >>+
> >>+/ {
> >>+	model = "Qualcomm Technologies, Inc. DB820c";
> >>+	compatible = "qcom,apq8096-sbc";
> >
> >I'm still not buying the concept of this being the one and only
> >single-board-computer.
> >
> +1
> 
> AFAIK, The problem is the dtbTool. dtbTool has predefined all the platform
> names along with its platform ID's [1] for auto generating board-id, pmic-id
> and soc-id. dtbTool checks the compatible strings along with soc name with
> its static list, it would fail if it did not find a matching combination of
> soc,platform compatible.
> 
> Either we have to cope up with this and have a compatbile strings which keep
> dtbTool happy
>  or
> Keep patching dtbtool to be more flexible.

dtbTool is unfortunately broken if it can't handle unknown compatibles.

> 
> There is another problem with dtbTool, We can not use dtbTool with new
> boards from other vendors with own board names, like SD600 or IFC6410 and
> so..
> 

Which means that everyone will, just like in Android-land, ship their
products with the one-and-only-supported qcom,apq8096-sbc.

If at least dtbTool would skip (and potentially warn about) unknown
entries vendors could add their specific name and then have the sbc
compatible, allowing for compatibility while dtbTool is updated.

> 
> IMO, we should patch dtbTool to make it more flexible to cope up with
> situations like this.
> 
> >If this compatible fully and exclusively identifies this particular
> >board then dtbTool should be updated to follow the product name
> >"qcom,apq8096-db820c". If on the other hand this identifies a class of
> >single-board-computers, then the compatible should list both
> >"qcom,apq8096-dtb820c" and "qcom,apq8096-sbc".
> 
> Am not sure this would actually work when we have two boards with same sbc
> platform ID. Which one would the bootloader pick? and on what basis?
> 

In Android land you don't have this problem, you know which zImage and
which set of dtbs you should put into your boot.img. So based on above
problem (requirement to update dtbTool) and the lack of need companies
will continue to ship their products as "mtp" or "sbc".

Regards,
Bjorn