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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1cbafa2a-fe9e-04ec-35cc-d675a781a5b6@gmail.com>
Date:   Wed, 20 Jan 2021 23:45:23 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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 1/20/21 11:34 PM, Viresh Kumar wrote:
> 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.

I have only the most surface knowledge of fdtoverlay, mostly from
"fdtoverlay --help", but you can apply multiple overlays with a
single invocation of fdtoverlay.  My _assumption_ was that the
overlays would be applied in order, and after any given overlay
was applied, subsequent overlays could reference the previously
applied overlay.

Is my assumption incorrect?

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