Re: [PATCH V2] nvmem: add explicit config option to read OF fixed cells

From: Michael Walle <michael@walle.cc>
To: zajec5@gmail.com
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	Michael Walle <michael@walle.cc>
Subject: Re: [PATCH V2] nvmem: add explicit config option to read OF fixed cells
Date: Thu,  9 Mar 2023 10:40:10 +0100	[thread overview]
Message-ID: <20230309094010.1051573-1-michael@walle.cc> (raw)
In-Reply-To: <20230224072903.20945-1-zajec5@gmail.com>

[as this mentions  nvmem layouts it would have been nice to include me]

> NVMEM subsystem looks for fixed NVMEM cells (specified in DT) by
> default. This behaviour made sense in early days before adding support
> for dynamic cells.

Why is that? It still makes sense, doesn't it?

> With every new supported NVMEM device with dynamic cells current
> behaviour becomes non-optimal. It results in unneeded iterating over DT
> nodes and may result in false discovery of cells (depending on used DT
> properties).

What false discoveries?

> This behaviour has actually caused a problem already with the MTD
> subsystem. MTD subpartitions were incorrectly treated as NVMEM cells.

But this is solved, correct?

> Also with upcoming support for NVMEM layouts no new binding or driver
> should support fixed cells defined in device node.

How would you support older device trees with newer kernels or the
other way around? I'm not sure I get your motivation to drop handling
the fixed cells.

> Solve this by modifying drivers for bindings that support specifying
> fixed NVMEM cells in DT. Make them explicitly tell NVMEM subsystem to
> read cells from DT.

How can a driver know when there are fixed cells and when not? IOW.
only new ones can be affected.

If you want to get rid of the schema for *new* drivers then what
about having a new child node, something like "nvmem-fixed-cells",
similar to "nvmem-layout".

And then you'd tell the new drivers to use the new-style dt binding. But
there are no new drivers yet. So I'm still not sure I get your motivation.

-michael

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