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From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Michael Walle <michael@walle.cc>
Cc: "Richard Weinberger" <richard@nod.at>,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Srinivas Kandagatla" <srinivas.kandagatla@linaro.org>,
	"Shawn Guo" <shawnguo@kernel.org>, "Li Yang" <leoyang.li@nxp.com>,
	"Rafał Miłecki" <rafal@milecki.pl>,
	"Frank Rowand" <frowand.list@gmail.com>,
	linux-mtd@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	"Ahmad Fatoum" <a.fatoum@pengutronix.de>,
	"Philipp Zabel" <p.zabel@pengutronix.de>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Robert Marko" <robert.marko@sartura.hr>
Subject: Re: [PATCH v2 00/20] nvmem: core: introduce NVMEM layouts
Date: Wed, 21 Sep 2022 11:58:13 +0200	[thread overview]
Message-ID: <20220921115813.208ff789@xps-13> (raw)
In-Reply-To: <20220901221857.2600340-1-michael@walle.cc>

Hi Michael, Srinivas,

+ Thomas and Robert

michael@walle.cc wrote on Fri,  2 Sep 2022 00:18:37 +0200:

> This is now the third attempt to fetch the MAC addresses from the VPD
> for the Kontron sl28 boards. Previous discussions can be found here:
> https://lore.kernel.org/lkml/20211228142549.1275412-1-michael@walle.cc/
> 
> 
> NVMEM cells are typically added by board code or by the devicetree. But
> as the cells get more complex, there is (valid) push back from the
> devicetree maintainers to not put that handling in the devicetree.
> 
> Therefore, introduce NVMEM layouts. They operate on the NVMEM device and
> can add cells during runtime. That way it is possible to add more complex
> cells than it is possible right now with the offset/length/bits
> description in the device tree. For example, you can have post processing
> for individual cells (think of endian swapping, or ethernet offset
> handling).
> 
> The imx-ocotp driver is the only user of the global post processing hook,
> convert it to nvmem layouts and drop the global post pocessing hook. Please
> note, that this change is only compile-time tested.

These layouts are an excellent idea. I actually have a new use case for
them. In modern Ethernet switches which follow the ONIE standard [1]
there is an nvmem device which contains a standardized
type-length-value array with many information about manufacturing and
mac addresses. There is no "static" pattern there and anyway so many
possible entries that it would be very tedious to list all of them in
the bindings, as each manufacturer chooses what it want to export on
each of its devices (although reading the data sequentially and
extracting the cells is rather straightforward).

Moreover, the specification [1] does not define any storage device
type, so it can be eg. an MTD device or an EEPROM. Having an
nvmem device provider separated from the nvmem cells provider makes
complete sense, the "layout" drivers idea proposed by Michael seem to be
a perfect fit.

Srinivas, can you give us an update on what you think about this
series (not a commitment, just how you feel it overall)?

Michael, is there a v3 in preparation? I'll try to write something on
top of your v2 otherwise.

> You can also have cells which have no static offset, like the
> ones in an u-boot environment. The last patches will convert the current
> u-boot environment driver to a NVMEM layout and lifting the restriction
> that it only works with mtd devices. But as it will change the required
> compatible strings, it is marked as RFC for now. It also needs to have
> its device tree schema update which is left out here. These two patches
> are not expected to be applied, but rather to show another example of
> how to use the layouts.

Actually I think these two matches make complete sense, right now one
can only use the u-boot-env cells if the environment is stored in an
mtd device, of course this covers many cases but not all of them and it
would be really nice to have this first layout example merged, not only
on the mailing list.

> For now, the layouts are selected by a specific compatible string in a
> device tree. E.g. the VPD on the kontron sl28 do (within a SPI flash node):
>   compatible = "kontron,sl28-vpd", "user-otp";
> or if you'd use the u-boot environment (within an MTD patition):
>   compatible = "u-boot,env", "nvmem";
> 
> The "user-otp" (or "nvmem") will lead to a NVMEM device, the
> "kontron,sl28-vpd" (or "u-boot,env") will then apply the specific layout
> on top of the NVMEM device.

Thanks,
Miquèl

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  parent reply	other threads:[~2022-09-21  9:59 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-01 22:18 [PATCH v2 00/20] nvmem: core: introduce NVMEM layouts Michael Walle
2022-09-01 22:18 ` [PATCH v2 01/20] net: add helper eth_addr_add() Michael Walle
2022-09-01 23:22   ` Randy Dunlap
2022-09-02  7:27     ` Michael Walle
2022-09-01 22:18 ` [PATCH v2 02/20] of: base: add of_parse_phandle_with_optional_args() Michael Walle
2022-09-01 22:18 ` [PATCH v2 03/20] nvmem: core: add an index parameter to the cell Michael Walle
2022-09-09  8:12   ` Srinivas Kandagatla
2022-09-01 22:18 ` [PATCH v2 04/20] nvmem: core: move struct nvmem_cell_info to nvmem-provider.h Michael Walle
2022-09-01 22:18 ` [PATCH v2 05/20] nvmem: core: drop the removal of the cells in nvmem_add_cells() Michael Walle
2022-09-01 22:18 ` [PATCH v2 06/20] nvmem: core: add nvmem_add_one_cell() Michael Walle
2022-09-09  8:52   ` Srinivas Kandagatla
2022-09-01 22:18 ` [PATCH v2 07/20] nvmem: core: use nvmem_add_one_cell() in nvmem_add_cells_from_of() Michael Walle
2022-09-01 22:18 ` [PATCH v2 08/20] nvmem: core: introduce NVMEM layouts Michael Walle
2022-09-01 22:18 ` [PATCH v2 09/20] nvmem: core: add per-cell post processing Michael Walle
2022-09-01 22:18 ` [PATCH v2 10/20] nvmem: core: allow to modify a cell before adding it Michael Walle
2022-09-01 22:18 ` [PATCH v2 11/20] nvmem: imx-ocotp: replace global post processing with layouts Michael Walle
2022-09-07 12:31   ` Michael Walle
2022-09-01 22:18 ` [PATCH v2 12/20] nvmem: cell: drop global cell_post_process Michael Walle
2022-09-01 22:18 ` [PATCH v2 13/20] nvmem: core: drop priv pointer in post process callback Michael Walle
2022-09-09  8:52   ` Srinivas Kandagatla
2022-09-09  8:58     ` Michael Walle
2022-09-09  9:08       ` Srinivas Kandagatla
2022-09-09  9:39         ` Michael Walle
2022-09-01 22:18 ` [PATCH v2 14/20] dt-bindings: mtd: relax the nvmem compatible string Michael Walle
2022-09-08 12:21   ` Krzysztof Kozlowski
2022-09-01 22:18 ` [PATCH v2 15/20] dt-bindings: nvmem: add YAML schema for the sl28 vpd layout Michael Walle
2022-09-08 12:22   ` Krzysztof Kozlowski
2022-09-12 19:20   ` Rob Herring
2022-09-13 14:21     ` Michael Walle
2022-09-22  9:22       ` Miquel Raynal
2022-09-01 22:18 ` [PATCH v2 16/20] nvmem: layouts: add sl28vpd layout Michael Walle
2022-09-01 22:18 ` [PATCH v2 17/20] nvmem: core: export nvmem device size Michael Walle
2022-09-01 22:18 ` [PATCH v2 18/20] arm64: dts: ls1028a: sl28: get MAC addresses from VPD Michael Walle
2022-09-01 22:18 ` [RFC PATCH v2 19/20] nvmem: layouts: rewrite the u-boot-env driver as a NVMEM layout Michael Walle
2022-09-21 10:37   ` Miquel Raynal
2022-09-01 22:18 ` [RFC PATCH v2 20/20] nvmem: layouts: u-boot-env: add device node Michael Walle
2022-09-21  9:58 ` Miquel Raynal [this message]
2022-09-22 21:22   ` [PATCH v2 00/20] nvmem: core: introduce NVMEM layouts Srinivas Kandagatla
2022-09-23  8:31     ` Miquel Raynal
2022-09-23 15:47 ` Miquel Raynal
2022-09-23 17:28   ` Michael Walle

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