[RFC] dtc: add ability to make nodes conditional on them being referenced

[Lothar Waßmann]

Hi,

Heiko Stübner wrote:
> From: Heiko Stuebner <heiko.stuebner at bqreaders.com>
> 
> On i.MX, which carries a lot of pin-groups of which most are unused on
> individual boards, they noticed that this plehora of nodes also results
> in the runtime-lookup-performance also degrading [0].
> 
> A i.MX-specific solution defining the pingroups in the board files but
> using macros to reference the pingroup-data was not well received
> 
> This patch is trying to solve this issue in a more general way, by
> adding the ability to mark nodes as needing to be referenced somewhere
> in the tree.
> 
> To mark a node a needing to be referenced it must be prefixed with
> /delete-unreferenced/. This makes dtc check the nodes reference-status
> when creating the flattened tree, dropping it if unreferenced.
> 
> For example, the i.MX6SL pingroup
> 
> 	/delete-uneferenced/ pinctrl_ecspi1_1: ecspi1grp-1 {
                 ^^
s/unef/unref/
not really important here, but bad for copy/pasters


Lothar Waßmann
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