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hwmon: Serialize accesses in hwmon core

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Implement locking in the hardware monitoring core for drivers using
the _with_info() API functions.

Most hardware monitoring drivers need to support locking to protect
against parallel accesses from userspace. With older API functions, such
locking had to be implemented in the driver code since sysfs attributes
were created by the driver. However, the _with_info() API creates sysfs
attributes in the hardware monitoring core. This makes it easy to move
the locking primitives into that code. This has the benefit of simplifying
driver code while at the same time reducing the risk of incomplete of bad
locking implementations in hardware monitoring drivers.

While this means that all accesses are forced to be synchronized, this
has little if any practical impact since accesses are expected to be low
frequency and are typically synchronized from userspace anyway since
only a single process is accessing the data. On top of that, many drivers
use regmap, which also has its own locking scheme and already serializes
accesses.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Guenter Roeck
2025-06-05 16:23:57 -07:00
parent 90bad684e9
commit 3ad2a7b9b1
3 changed files with 48 additions and 7 deletions
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10
Documentation/hwmon/hwmon-kernel-api.rst
View File

@@ -42,6 +42,9 @@ register/unregister functions::
char *devm_hwmon_sanitize_name(struct device *dev, const char *name);
void hwmon_lock(struct device *dev);
void hwmon_unlock(struct device *dev);
hwmon_device_register_with_info registers a hardware monitoring device.
It creates the standard sysfs attributes in the hardware monitoring core,
letting the driver focus on reading from and writing to the chip instead
@@ -79,6 +82,13 @@ devm_hwmon_sanitize_name is the resource managed version of
hwmon_sanitize_name; the memory will be freed automatically on device
removal.
When using ``[devm_]hwmon_device_register_with_info()`` to register the
hardware monitoring device, accesses using the associated access functions
are serialised by the hardware monitoring core. If a driver needs locking
for other functions such as interrupt handlers or for attributes which are
fully implemented in the driver, hwmon_lock() and hwmon_unlock() can be used
to ensure that calls to those functions are serialized.
Using devm_hwmon_device_register_with_info()
--------------------------------------------