linux-kernel - [PATCH 0/6] i2c: provide and use i2c_adapter

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Message-Id: <20251223-i2c-adapter-dev-wrapper-v1-0-bcf960a48fa9@oss.qualcomm.com>
Date: Tue, 23 Dec 2025 11:08:17 +0100
From: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Jean Delvare <jdelvare@...e.com>, Andi Shyti <andi.shyti@...nel.org>,
        Shyam Sundar S K <shyam-sundar.s-k@....com>,
        Nirujogi Pratap <pratap.nirujogi@....com>, Bin Du <bin.du@....com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jan Dabros <jsd@...ihalf.com>,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        Hans Hu <hanshu@...oxin.com>
Cc: Bartosz Golaszewski <brgl@...nel.org>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
Subject: [PATCH 0/6] i2c: provide and use i2c_adapter_dev()

It's been another year of discussing the object life-time problems at
conferences. I2C is one of the offenders and its problems are more
complex than those of some other subsystems. It seems the revocable[1]
API may make its way into the kernel this year but even with it in
place, I2C won't be able to use it as there's currently nothing to
*revoke*. The struct device is embedded within the i2c_adapter struct
whose lifetime is tied to the provider device being bound to its driver.

Fixing this won't be fast and easy but nothing's going to happen if we
don't start chipping away at it. The ultimate goal in order to be able
to use an SRCU-based solution (revocable or otherwise) is to convert the
embedded struct device in struct i2c_adapter into an __rcu pointer that
can be *revoked*. To that end we need to hide all dereferences of
adap->dev in drivers.

Other series address more generic problems - like printk helpers and
parent/of_node setting - but there are still some more specific
use-cases of drivers dereferencing the internal struct device of
i2c_adapters. We need to hide the fact that the device is embedded in
i2c_adapter before we can move it out so provide a helper that provides
the address of struct device without showing how it's stored and use it
in some drivers.

[1] https://lore.kernel.org/all/20251106152330.11733-1-tzungbi@kernel.org/

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>
---
Bartosz Golaszewski (6):
      i2c: provide i2c_adapter_dev()
      i2c: piix4: use i2c_adapter_dev()
      i2c: amd-asf-plat: use i2c_adapter_dev()
      i2c: designware-amdisp: use i2c_adapter_dev()
      i2c: mv64xxx: use i2c_adapter_dev()
      i2c: viai2c-zhaoxin: use i2c_adapter_dev()

 drivers/i2c/busses/i2c-amd-asf-plat.c      | 4 ++--
 drivers/i2c/busses/i2c-designware-amdisp.c | 2 +-
 drivers/i2c/busses/i2c-mv64xxx.c           | 4 ++--
 drivers/i2c/busses/i2c-piix4.c             | 6 +++---
 drivers/i2c/busses/i2c-viai2c-zhaoxin.c    | 2 +-
 include/linux/i2c.h                        | 5 +++++
 6 files changed, 14 insertions(+), 9 deletions(-)
---
base-commit: 9448598b22c50c8a5bb77a9103e2d49f134c9578
change-id: 20251222-i2c-adapter-dev-wrapper-c882660190a2

Best regards,
-- 
Bartosz Golaszewski <bartosz.golaszewski@....qualcomm.com>