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    SubjectRe: [linux-pm] suspend blockers & Android integration
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    On Fri, 2010-06-11 at 10:46 -0400, Alan Stern wrote:
    > On Fri, 11 Jun 2010, James Bottomley wrote:
    >
    > > On Thu, 2010-06-10 at 21:21 -0700, David Brownell wrote:
    > > > Do we at least have a clean way that a driver can
    > > > reject a system suspend? I've lost track of many
    > > > issues, but maybe this could be phrased as a QOS
    > > > constraint: the current config of driver X needs
    > > > clock Y active to enter the target system suspend
    > > > state, driver's suspend() method reports as much. Then the entry to
    > > > that system state gets blocked
    > > > if the clock isn't enabled.
    > >
    > > So in QoS modifications to android patches, the answer is "yes" ...
    > > except that the current android patch set didn't actually have this type
    > > of wakelock in it.
    > >
    > > Android wants an idleness suspend block (or pm qos constraint) that a
    > > driver can set to prevent the system idleness power govenor from
    > > dropping into a power state too low for the driver, so in USB terms this
    > > would prevent the states that shut down the clock. For android, it
    > > prevented shutdown of an internal i2c bus.
    > >
    > > The one thing that does look difficult is that these power constraints
    > > are device (and sometimes SoC) specific. Expressing them in a generic
    > > way for the cpu govenors to make sense of might be hard.
    >
    > Doesn't the clock framework already handle this sort of thing?

    Well, there are two elements to "this sort of thing":

    1. Allow a driver to request that a given clock not be turned off.
    2. Make the cpuidle governors aware of a pending "don't turn off X
    clock source" so they can keep the system in a state where the
    clock doesn't get powered down.

    As far as I can tell from the code, neither currently exists at the
    moment.

    James




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