linux-kernel - Re: nvmem: Defining cells on mtd created by mtdparts

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Date:   Fri, 15 Oct 2021 10:20:09 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Sven Eckelmann <sven@...fation.org>,
        openwrt-devel@...ts.openwrt.org
Cc:     Ansuel Smith <ansuelsmth@...il.com>,
        Michael Walle <michael@...le.cc>,
        Adrian Schmutzler <dev@...mutzler.it>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-mtd@...ts.infradead.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-kernel@...r.kernel.org
Subject: Re: nvmem: Defining cells on mtd created by mtdparts

On 11.10.2021 09:06, Sven Eckelmann wrote:
> 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.

I like the idea of connecting cmdline specified partitions (mtdparts=)
with DT. That will help devices that use DT at least.

One thing I'm not sure about is criteria. Ansuel in his patch
[PATCH] drivers: mtd: parsers: add nvmem support to cmdlinepart
https://gist.github.com/Ansuel/35abba1f5663ea3d9bd8eded01e8d95b
requires a matching name, offset & size.

I guess above may work for partitions that stay static like a
bootloader. What if someone wants to describe more dynamic partition
(firmware?). Should we reduce criteria to allow matching just by a
name?