Hi! A device that creates a child character device with cdev_device_add by default creates a PM sysfs group with power attributes for userspace control. This means that the power attributes monitors the child device only and thus does not reflect the parent device PM runtime behavior. But as the PM runtime framework (rpm_suspend/rpm_resume) operates not only on a single device that has been enabled for runtime PM, but also on its parent, it should be possible to synchronize the child and the parent so that the power attribute monitoring reflects the child and the parent as one. As an example, if an i2c_client device registers an iio_device, the iio_device will create sysfs power/attribute nodes for userspace control. But if the dev_pm_ops with resume/suspend callbacks is attached to the struct i2c_driver.driver.pm, the PM runtime needs to be enabled for the i2c_client device and not for the child iio_device. In this case PM runtime can be enabled for the i2c_client device and suspend/resume callbacks will be triggered, but the child sysfs power attributes will be visible but marked as 'unsupported' and can not be used for control or monitoring. This can be confusing as the sysfs device node presents the i2c_client and the iio_device as one device. A solution to this is to enable runtime PM not only for the i2c_device but for the iio_device child also. As there already exists a link from the child to its parent and both are enabled, all sysfs control/monitoring now reflects both devices, which from a userspace perspective makes more sense. These patches [1] adds a function to the PM runtime framework to synchronize the PM runtime enable state of a device with its parent, and [2] applies it to an iio device, where the described issue exists. Kind regards Mårten Lindahl Mårten Lindahl (2): PM: runtime: Synchronize PM runtime enable state with parent iio: light: vcnl4000: Incorporate iio_device with PM runtime drivers/base/power/runtime.c | 18 ++++++++++++++++++ drivers/iio/light/vcnl4000.c | 1 + include/linux/pm_runtime.h | 2 ++ 3 files changed, 21 insertions(+) -- 2.30.2
