From:   Michael Walle <michael@walle.cc>
To:     zajec5@gmail.com
Cc:     a.zummo@towertech.it, agross@kernel.org,
        alexandre.belloni@bootlin.com, alexandre.torgue@foss.st.com,
        alyssa@rosenzweig.io, andersson@kernel.org,
        angelogioacchino.delregno@collabora.com, asahi@lists.linux.dev,
        baolin.wang@linux.alibaba.com, claudiu.beznea@microchip.com,
        festevam@gmail.com, hayashi.kunihiko@socionext.com,
        heiko@sntech.de, jbrunet@baylibre.com, jernej.skrabec@gmail.com,
        kernel@pengutronix.de, khilman@baylibre.com,
        konrad.dybcio@linaro.org, linux-amlogic@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org,
        linux-arm-msm@vger.kernel.org, linux-imx@nxp.com,
        linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org,
        linux-mtd@lists.infradead.org, linux-rockchip@lists.infradead.org,
        linux-rtc@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com,
        linux-sunxi@lists.linux.dev, marcan@marcan.st,
        martin.blumenstingl@googlemail.com, matthias.bgg@gmail.com,
        mcoquelin.stm32@gmail.com, mhiramat@kernel.org,
        michal.simek@xilinx.com, miquel.raynal@bootlin.com,
        neil.armstrong@linaro.org, orsonzhai@gmail.com, rafal@milecki.pl,
        richard@nod.at, s.hauer@pengutronix.de, samuel@sholland.org,
        shawnguo@kernel.org, srinivas.kandagatla@linaro.org,
        sven@svenpeter.dev, vigneshr@ti.com, vincent.sunplus@gmail.com,
        wens@csie.org, zbr@ioremap.net, zhang.lyra@gmail.com,
        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
Message-Id: <20230309094010.1051573-1-michael@walle.cc>
In-Reply-To: <20230224072903.20945-1-zajec5@gmail.com>
References: <20230224072903.20945-1-zajec5@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

[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