linux-kernel - [PATCH v3 0/2] nvmem: skip nodes with compatibles other than "nvmem-cell"

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Date:   Tue, 28 Apr 2020 13:18:25 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     kernel@...gutronix.de, ceggers@...i.de,
        Ahmad Fatoum <a.fatoum@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: [PATCH v3 0/2] nvmem: skip nodes with compatibles other than "nvmem-cell"

The nvmem cell binding applies to all objects which match "^.*@[0-9a-f]+$",
without taking a compatible into account. This precludes extension of e.g.
eeprom nodes by any child nodes other than nvmem. Consider following example:

	eeprom@0 {
		reg = <0 64>;
		#address-cells = <1>;
		#size-cells = <1>;

		partitions {
			compatible = "fixed-partitions";
			#address-cells = <1>;
			#size-cells = <1>;
			bits = <64 64 64>; /* to verify it's skipped */

			part@0 {
				reg = <0x00 16>;
			};
		};

		no-cell@10 {
			compatible = "not-nvmem-cell";
			reg = <0x10 4>;
			bits = <64 64 64>; /* to verify it's skipped */
		};

		cell-old@14 {
			reg = <0x14 0x2>;
		};

		cell-new@16 {
			compatible = "nvmem-cell";
			reg = <0x16 4>;
		};
	};

Without this series, the NVMEM driver interprets all direct children of eeprom@0
as NVMEM cells and driver probe fails, because the partitions node lacks a reg
property, e.g.:

  nvmem 0-00000: nvmem: invalid reg on /eeprom@0

Running dtbs_check on the snippet will skip partitions (it doesn't match above
regex), but will flag no-cell@10 and cell-new@16 as invalid.

With this series applied, the driver will skip partitions and no-cell@10,
because they have a compatible but it's not "nvmem-cell".
Both cell-old@14 and cell-new@16 will be interpreted as cells.

Likewise, running dtbs_check on the snippet will skip partitions (compatible
doesn't match and regex doesn't either) and no-cell@10, but accept the other two.

This series resolves an existing clash between this nvmem-cell binding and
the barebox bootloader binding that extends the fixed-partitions MTD
binding to EEPROMs[1]. It's also a building block for getting nvmem cells and
partitions in MTD devices to co-exist in the same device tree node[2].

The changes are backwards-compatible, because, per binding, a compatible
property in a cell node was so far invalid. More details in the commit
messages.

[1]: https://www.mail-archive.com/barebox@lists.infradead.org/msg33944.html
[2]: https://patchwork.ozlabs.org/patch/890741/

v2 -> v3:
  - use optional compatible property to weed out nodes instead of name
  - extend binding documentation (Srini)
v1 -> v2:
  - use ->full_name instead of ->name as to not break existing correct
    cells (Christian)

Cheers,
Ahmad Fatoum (2):
  dt-bindings: nvmem: skip nodes with compatibles other than
    "nvmem-cell"
  nvmem: core: skip nodes with compatibles other than "nvmem-cell"

 Documentation/devicetree/bindings/nvmem/nvmem.yaml | 14 +++++++++++++-
 drivers/nvmem/core.c                               |  4 ++++
 2 files changed, 17 insertions(+), 1 deletion(-)

Cc: Rob Herring <robh+dt@...nel.org>
Cc: devicetree@...r.kernel.org
-- 
2.26.2