Re: [PATCH 2/8] FIT: skip possible overlay config nodes

[Marco Felsch <m.felsch@pengutronix.de>]

Hi,

sorry for the delay on this patchset.

On 24-03-25, Sascha Hauer wrote:
> Hi Marco,
> 
> On Fri, Mar 22, 2024 at 05:49:47PM +0100, Marco Felsch wrote:
> > The FIT spec is not very specific when it comes to device-tree overlay
> > handling.
> 
> By FIT spec you mean
> https://github.com/u-boot/u-boot/blob/master/doc/usage/fit/overlay-fdt-boot.rst,
> right, or is there more?

this is just an example which is not complete e.g. it misses the
signature node in case of verified boot. I used [1] as reference but
after reading it again I see that this reference list the kernel or
firmware properties as mandatory.

[1] https://docs.u-boot.org/en/latest/usage/fit/source_file_format.html#configurations-node

> > Overlays can be added directely to an config node:
> > 
> > 	config-a {
> > 		compatible = "machine-compatible";
> > 		kernel = "kernel-img-name";
> > 		fdt = "fdt-base-name", "fdt-overlay1-name", "...";
> > 	}
> > 
> > or they are supplied via dedicated config nodes:
> > 
> > 	overlay-2 {
> > 		fdt = "fdt-overlay2-name";
> > 	}
> > 
> > Of course these config nodes can have compatibles as well:
> > 
> > 	overlay-3 {
> > 		compatible = "machine-compatible";
> > 		fdt = "fdt-overlay3-name";
> > 	}
> 
> The text I referenced above doesn't mention compatible properties in
> overlay config nodes.

You're right, but the format description chapter [1] does.

> > The current fit_find_compatible_unit() code would skip the overlay node
> > if the config-a compatible has the same score as the overlay-3
> > compatible and if the overlay-3 config-node is listed after the config-a
> > config-node. But if the compatible of config-a config-node has a lower
> > score or the overlay-3 config-note is listed first (the spec does not
> > specify any order) we end up in taking the overlay-3 config-node instead
> > of config-a config-node.
> 
> You could distinguish overlay config nodes from full config nodes by the
> presence of a "kernel" property. Overlay config nodes do not have it.

Of course this could be done but I wanted to make it more explicit since
the FIT spec is not very clear when it comes to overlays. Instead of
adding an explicit image type like:

  - type = "flat_dt_overlay";

they used the already existing definitions. Therefore I went this way so
it is up to user to specify the overlay config nodes explicit.

Regards,
  Marco

> 
> Sascha
> 
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