linux-kernel - Re: [PATCH 06/12] arm64: dts: zynqmp: Add label for zynqmp

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Message-ID: <X86poiQSzv5Uva1r@pendragon.ideasonboard.com>
Date:   Tue, 8 Dec 2020 00:16:02 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     linux-kernel@...r.kernel.org, monstr@...str.eu, git@...inx.com,
        Kalyani Akula <kalyani.akula@...inx.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Manish Narani <manish.narani@...inx.com>,
        Rajan Vaja <rajan.vaja@...inx.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 06/12] arm64: dts: zynqmp: Add label for zynqmp_ipi

Hi Michal,

On Mon, Dec 07, 2020 at 10:39:25AM +0100, Michal Simek wrote:
> On 06. 12. 20 23:46, Laurent Pinchart wrote:
> > On Wed, Dec 02, 2020 at 03:06:05PM +0100, Michal Simek wrote:
> >> Add label which is used by bootloader for adding bootloader specific flag.
> >>
> >> Signed-off-by: Michal Simek <michal.simek@...inx.com>
> >> ---
> >>
> >> U-Boot needs to add u-boot,dm-pre-reloc; property
> > 
> > I'm not entirely sure what best practice rules are in this area, but
> > shouldn't U-Boot locate the node by name instead of label ?
> 
> Labels are not listed in dt binding and there are two approaches how to
> reference nodes. Via full path with node name or via labels.
> I do normally use labels which are much simple.

Note that labels require the DTB to be compiled with the -@ option,
otherwise they're not present in the binary.

> And also if you take a look how dtb looks like (convert back to dts) you
> can see that for example aliases are using full path (just &label) but
> clocks/gic which is the part of <> is handled via phandles as numbers.
> 
> And labels names can vary and shouldn't be the part of binding doc as
> far as I know. But I can be wrong of course.

The DT bindings should document the interface with the operating system,
and if applicable, the boot loader. If the boot loader requires a
particular label, then it becomes part of the ABI, and I think it should
be documented in the bindings.

-- 
Regards,

Laurent Pinchart