linux-kernel - Re: [PATCH 1/2] arm64: dts: allwinner: Olimex A64-OLinuXino: enable eMMC.

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Date:   Thu, 27 Sep 2018 11:49:20 -0300
From:   Rodrigo Exterckötter Tjäder 
        <rodrigo@...der.xyz>
To:     maxime.ripard@...tlin.com
Cc:     wens@...e.org, robh+dt@...nel.org, mark.rutland@....com,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: dts: allwinner: Olimex A64-OLinuXino: enable eMMC.

On Thu, Sep 27, 2018 at 5:17 AM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Tue, Sep 25, 2018 at 02:47:59PM -0300, Rodrigo Exterckötter Tjäder wrote:
> > On Tue, Sep 25, 2018 at 6:01 AM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > > We can't really do that, unfortunately. If the device tree name was to
> > > change for a given board, we'd break all the build systems, boot
> > > scripts and distros out there.
> >
> > What if we keep the device tree for the version without WiFi and eMMC
> > with the current name and create new device trees for the other two
> > versions?
>
> Wifi and Bluetooth should be dealt with with overlays in this case,
> and since the eMMC is already enabled, then there's nothing to do, I
> guess.

It's WiFi that is already enabled, not eMMC. Only one of the three
variants has WiFi.

We can't even remove a node from a device tree? Removing the WiFi node
from the current tree would make it correspond to the variant with the
least features.

About device tree overlays, I read overlay-notes.txt, but I went
looking for an example with "git grep /plugin/ arch" and it came
empty. Is this approach not used for other boards?

Does the overlay approach make the device available at boot time? That
is important for a storage device such as eMMC.

I went with the separate dts approach because that's what I saw was
done for other similar cases, like Pine64 and Pine64+, OLinuXino-LIME2
and its variant with eMMC, among others.