linux-kernel - [PATCH v2 2/6] nvmem: specify ->reg_read/reg

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Message-Id: <20241209-rmem-v2-2-cbc0e8c08a21@bootlin.com>
Date: Mon, 09 Dec 2024 16:59:36 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Nicolas Saenz Julienne <nsaenz@...nel.org>, 
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-mips@...r.kernel.org, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Grégory Clement <gregory.clement@...tlin.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>
Subject: [PATCH v2 2/6] nvmem: specify ->reg_read/reg_write() expected
 return values

Both ->reg_read() and ->reg_write() return values are not easy to
deduce. Explicit that they should return zero on success (and negative
values otherwise).

Such callbacks, in some alternative world, could return the number of
bytes in the success case. That would be translated to errors in the
nvmem core because of checks like:

	ret = nvmem->reg_write(nvmem->priv, offset, val, bytes);
	if (ret) {
		// error case
	}

This mistake is not just theoretical, see commit
28b008751aa2 ("nvmem: rmem: Fix return value of rmem_read()").

Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
---
 include/linux/nvmem-provider.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 3ebeaa0ded00c8d12230e5be7eed045a89a82669..515676ebe59875fa0ab8a4e772542bdc90ead8e3 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -92,8 +92,8 @@ struct nvmem_cell_info {
  * @read_only:	Device is read-only.
  * @root_only:	Device is accessibly to root only.
  * @of_node:	If given, this will be used instead of the parent's of_node.
- * @reg_read:	Callback to read data.
- * @reg_write:	Callback to write data.
+ * @reg_read:	Callback to read data; return zero if successful.
+ * @reg_write:	Callback to write data; return zero if successful.
  * @size:	Device size.
  * @word_size:	Minimum read/write access granularity.
  * @stride:	Minimum read/write access stride.

-- 
2.47.1