Re: Hotplug events for system suspend/resume

From: Todd Poynor
Date: Wed May 12 2004 - 14:41:31 EST

Nigel Cunningham wrote:

You're thinking ACPI drivers initiating a suspend? They would do it through acpid, wouldn't they? At least that's the glue I use to get my sleep button to initiate a suspend. I would assume thermal events would/should work the same.

Hi, my main interest is embedded platforms that may or (usually) do not implement ACPI. Therefore, part of what I've been generally driving at is that there may be value to adding support for these sorts of kernel-to-userspace notifiers in the generic power layer. As I understand it (and I might be behind the times here, please do correct me if I'm wrong), acpid reads ACPI-specific power event notifiers, such as button pressed, thermal limit exceeded, etc. from the kernel via /proc, and acpid executes scripts in /etc/acpi/ to handle the event. Some of the embedded developers I deal with have asked for similar notifiers in a non-ACPI context. The system suspend/resume notifiers discussed in this thread could be thought of as a general form of "sleep button pressed" type event. (And I now realize it may have been better to implement and pitch it as such.)

So, independently of the merits of any particular event notification, it may be worth discussing whether there's advantages to using the hotplug mechanism for userspace notification and script execution for power events, and hooked into the generic power subsystem. The likely alternative is that acpid continues doing things its way and non-ACPI systems do something rather different (we already have acpid-like event notifiers via sysfs attributes and I'm trying to get rid of them). Not that this ranks among the most pressing of issues facing Linux today, but since a generic power subsystem has been created, and since it takes some steps toward abstracting away various ACPI specifics, I think there's arguably some benefit to taking this particular step as well. An acpid-like interface (or even directly adapting acpid) for non-ACPI systems is another possibility.

I'd be happy to discuss this further if there's interest. Thanks -- Todd
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