linux-kernel - [PATCH 0/4] hwmon: Update handling of chip-id enums

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Date: Mon, 10 Jun 2024 11:10:42 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: linux-hwmon@...r.kernel.org
Cc: Rob Herring <robh@...nel.org>,
	linux-kernel@...r.kernel.org,
	Peter Yin <peteryin.openbmc@...il.com>,
	Potin Lai <potin.lai.pt@...il.com>,
	Daniel Matyas <daniel.matyas@...log.com>,
	Andrew Davis <afd@...com>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 0/4] hwmon: Update handling of chip-id enums

With the transition to use device_get_match_data() or i2c_get_match_data()
instead of i2c_match_id() and of_match_device(), the assumption was made
that the data pointer in struct i2c_device_id and struct of_device_id must
not be NULL (0). Initial patches changed enums used in those data pointers
to start with 1.

However, it turns out that this is only necessary if device_get_match_data()
is used. i2c_get_match_data() calls device_get_match_data() and uses
i2c_match_id() as fallback if device_get_match_data() returns NULL.
Therefore, it is perfectly valid to keep using 0 as starting enum value
as long as struct i2c_device_id is complete and matches the data in struct
of_device_id.

It is confusing to have some drivers start enums with 0 and others starting
them with 1, even more so if that is done inconsistently and/or if enums
starting with 1 are used to index arrays. Let enums start with index 0
where possible, and otherwise explain why the index has to start with 1.

----------------------------------------------------------------
Guenter Roeck (4):
      hwmon: (pmbus/lm25066) Let enum chips start with index 0
      hwmon: (nct6775) Let enum kinds start with index 0
      hwmon: (pmbus/mp2856) Let enum chips start with index 0
      hwmon: (pmbus/max31827) Explain why enum chips must not start with 0

 drivers/hwmon/max31827.c      | 5 +++++
 drivers/hwmon/nct6775.h       | 2 +-
 drivers/hwmon/pmbus/lm25066.c | 2 +-
 drivers/hwmon/pmbus/mp2856.c  | 8 ++++----
 4 files changed, 11 insertions(+), 6 deletions(-)