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

From: Frank Rowand
Date: Thu Jan 21 2021 - 00:46:37 EST

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.