nvmem: Defining cells on mtd created by mtdparts

[Sven Eckelmann]

On Sunday, 10 October 2021 14:53:13 CEST Sven Eckelmann wrote:
[...]
> Since there are most likely more devices out there which use mtdparts, I would 
> guess that there might already be a strategy out there which can be used to 
> define the nvmem-provider for mtdparts defined partitions. At least I saw that 
> Bartosz Golaszewski added all the mtd devices automatically as nvmem provider 
> in c4dfa25ab307 ("mtd: add support for reading MTD devices via the nvmem 
> API"). So there might also be something for nvmem-cells to find the correct 
> mtd instead of relying on the fixed-partitions registration + of_node (which 
> doesn't exist because it comes from mtdparts and not devicetree).

Ansuel Smith just proposed in OpenWrt [1] a workaround. It basically adds a 
minimal fixed-partitions parser to the mtd cmdlinepart parser (responsible for 
the mtdparts=) that tries to find the matching (size + offset) fixed-partition 
from the devicetree. The code in mtd_device_parse_register
(add_mtd_partitions -> add_mtd_device -> mtd_nvmem_add) will then 
automatically take care of the rest.

Kind regards,
	Sven

[1] https://github.com/openwrt/openwrt/pull/4664#issuecomment-939567963
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