Re: [RFD] How to tell ACPI drivers what the target sleep state is (was: Re: [PATCH 1/2] acpi choose sleep state help)

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On Thursday 21 June 2007, Rafael J. Wysocki wrote:
> The issue at hand is that some device drivers may need to know what the
> target sleep state of the system will be when their .suspend() routines are
> being executed.  Currently, there's no means of passing that information to the
> drivers and my question is how to do this.

Actually what they need to know is some *attribute* of that state.

They really don't care what the state is.  The $SUBJECT patch isn't
driver code ... it's for platform hooks that expose attributes to
the drivers.  Specifically, it's ACPI code, talking to drivers that
must run on non-ACPI systems.  Any driver that thinks it needs to
understand anything about ACPI states is sadly broken.

Remember also that the Linux "states" (in /sys/power/state) are an
inadequate representation of what most hardware can do.  Common
hardware can support a lot more low power sleep modes than the two
states Linux currently defines ... a limitation inherited from
first APM, and them more recently ACPI, which doesn't fit embedded
systems well at all.

- Dave


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