linux-kernel - Re: [PATCH V5 5/5] of: unittest: Statically apply overlays using fdtoverlay

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Message-ID: <20210121053426.4dw5oqz7qb4y7hvm@vireshk-i7>
Date:   Thu, 21 Jan 2021 11:04:26 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     David Gibson <david@...son.dropbear.id.au>,
        Rob Herring <robh+dt@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bill Mills <bill.mills@...aro.org>, anmar.oueja@...aro.org
Subject: Re: [PATCH V5 5/5] of: unittest: Statically apply overlays using
 fdtoverlay

On 20-01-21, 23:14, Frank Rowand wrote:
> It is a convenient FDT to use because it provides the frame that the overlays
> require to be applied.  It is fortunate that fdtoverlay does not reject the use
> of an FDT with overlay metadata as the base blob.

> This is probably a good idea instead of depending on the leniency of fdtoverlay.

I believe fdtoverlay allows that intentionally, that would be required
for the cases where we have a hierarchy of extension boards or
overlays.

A platform can have a base dtb (with /plugin/;), then we can have an
overlay (1) for an extension board (with /plugin/;) and then an
overlay (2) for an extension board for the previous extension board.

In such a case overlay-(2) can't be applied directly to the base dtb
as it may not find all the nodes it is trying to update. And so
overlay-(2) needs to be applied to overlay-(1) and then the output of
this can be applied to the base dtb.

This is very similar to what I tried with the intermediate.dtb
earlier.

-- 
viresh