linux-kernel - Re: [PATCH 3/4] ARM: tegra: nyan-big: Include compatible revisions for proper detection

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Date:   Tue, 20 Sep 2016 20:02:24 +0200
From:   Paul Kocialkowski <contact@...lk.fr>
To:     Jon Hunter <jonathanh@...dia.com>, linux-kernel@...r.kernel.org
Cc:     devicetree@...r.kernel.org, Stephen Warren <swarren@...dotorg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-tegra@...r.kernel.org, Alexandre Courbot <gnurou@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] ARM: tegra: nyan-big: Include compatible revisions
 for proper detection

Le mardi 20 septembre 2016 à 18:56 +0100, Jon Hunter a écrit :
> On 20/09/16 18:53, Paul Kocialkowski wrote:
> > 
> > * PGP Signed by an unknown key
> > 
> > Le mardi 20 septembre 2016 à 18:41 +0100, Jon Hunter a écrit :
> > > 
> > > On 28/08/16 18:32, Paul Kocialkowski wrote:
> > > > 
> > > > 
> > > > Depthcharge (the payload used with cros devices) will attempt to detect
> > > > boards using their revision. This includes all the known revisions for
> > > > the nyan-big board so that the dtb can be selected preferably.
> > > 
> > > May be I am missing something here, but for the mainline there is only
> > > one dtb available and so why is this needed for the mainline?
> > 
> > There is indeed a single dts in mainline, but depthcharge will use the
> > revision
> > to match the compatible string (e.g. it will look for google,nyan-big-rev5,
> > not
> > google,nyan-big), so we need to list them all in that single dts. Otherwise,
> > depthcharge will fall back to the default config, which may or may not be
> > suitable for nyan.
> 
> Is tegra124-nyan-big.dtb not the default?

You can't expect that to always be the case. The image format allows many
different dts to be provided, so I could easily build with multi_v7_defconfig
and have various dts for various devices in the same image, and just select a
random one as default.

Here, default is really a fallback, the right one is expected to be detected by
this mechanism. And it really doesn't hurt to provide that information for
proper detection.

Note that this is done with many other cros devices in mainline (such as rk3288
veyrons).

-- 
Paul Kocialkowski, developer of low-level free software for embedded devices

Website: https://www.paulk.fr/
Coding blog: https://code.paulk.fr/
Git repositories: https://git.paulk.fr/ https://git.code.paulk.fr/
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