On Sat, 20 Aug 2011, Mark Brown wrote:

On Fri, Aug 19, 2011 at 10:24:19PM -0400, Alan Stern wrote:

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On Sat, 20 Aug 2011, Mark Brown wrote:

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interfaces and let the subsystem and driver translate these into actual
wakeup latency constraints:

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  https://lists.linux-foundation.org/pipermail/linux-pm/2011-August/032422.html
  https://lists.linux-foundation.org/pipermail/linux-pm/2011-August/032428.html

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This is much easier for users as it translates into something they're
actually doing (and in most cases the driver can make it Just Work) and
it means that off the shelf applications will end up tuning the system
appropriately by themselves.  I'm additionally concerned that if we
expose this stuff directly to userspace that's an open invitation to
driver authors to not even bother trying to make the kernel figure this
stuff out by itself and to instead tie the system together with magic
userspace.

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Can you give a couple of examples to illustrate these points?  I think
it would help a lot to make the conversation more concrete.

Examples of what?  Latency constraints from drivers?  That'd be things
like Kevin listed in the second message linked above - the kernel knows
it needs to wake up within a given time period in order to have time to
do what it needs to do in response to a given wake source such as
filling a buffer before it underflows.

No, I as wasking about driver- and subsystem-specific interfaces to
userspace that translate into things users are already doing.  Kevin's
example was a touchscreen (although that was really an example of
setting a power usage level, not a latency constraint).  Do you have
any others?

Alan Stern