On Monday, September 07, 2015 11:42:41 PM Irina Tirdea wrote:

Add new option to sysfs control interface, allowing the user to force
suspend the device.

Had we thought this had been a good idea, we'd have added that thing to
the interface from the start.

The problem with it is that user space generally doesn't know when it is
safe to suspend a device, so it cannot force anything into runtime suspend.

This is useful for devices that need to be
suspended when closing the lid of a laptop or the screen of a mobile
device, while userspace still holds open handles to it and the
system does not enter system suspend.

Add the "off" option to the sysfs control power interface, along with
the already present "on" and "auto". When this attribute is set to
"off", the device will be force suspended by calling its runtime
suspend callback and disabling runtime power management so that
further acceses to the device will not change the actual state.

And how is user space supposed to know that it doesn't break things
this way?

The device can be resumed by setting the attribute to "on" or "auto".
The behaviour of the interface when switching only between "on"
and "auto" states remains unchanged.

Signed-off-by: Irina Tirdea <redacted>
---

Hi,

This is a proposal for suspending devices when the closing the lid of
a laptop or the screen of a mobile device.

I am testing this with a Goodix touchscreen [1] for an Android mobile
device. Android has an userspace layer (power HAL) that would normally
close the touchscreen when the screen is closed. Android touchscreen
drivers usually provide a custom sysfs interface to allow this.
This would be better implemented in a common place, to avoid code
duplication and to simplify the driver code (as previosly discussed
in [1]).

I know there are more ways to implement this, so I would appreciate
your feedback.

So the feedback is that this is not going to work in general.  Please
use a different approach.

Thanks,
Rafael