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    Subjectcpuidle future and improvements

    Dear all,

    A few weeks ago, Peter De Schrijver proposed a patch [1] to allow per
    cpu latencies. We had a discussion about this patchset because it
    reverse the modifications Deepthi did some months ago [2] and we may
    want to provide a different implementation.

    The Linaro Connect [3] event bring us the opportunity to meet people
    involved in the power management and the cpuidle area for different SoC.

    With the Tegra3 and big.LITTLE architecture, making per cpu latencies
    for cpuidle is vital.

    Also, the SoC vendors would like to have the ability to tune their cpu
    latencies through the device tree.

    We agreed in the following steps:

    1. factor out / cleanup the cpuidle code as much as possible
    2. better sharing of code amongst SoC idle drivers by moving common bits
    to core code
    3. make the cpuidle_state structure contain only data
    4. add a API to register latencies per cpu

    These four steps impacts all the architecture. I began the factor out
    code / cleanup [4] and that has been accepted upstream and I proposed
    some modifications [5] but I had a very few answers.

    The patch review are very slow and done at the last minute at the merge
    window and that makes code upstreaming very difficult. It is not a
    reproach, it is just how it is and I would like to propose a solution
    for that.

    I propose to host a cpuidle-next tree where all these modifications will
    be and where people can send patches against, preventing last minutes
    conflicts and perhaps Lenb will agree to pull from this tree. In the
    meantime, the tree will be part of the linux-next, the patches will be
    more widely tested and could be fixed earlier.

    -- Daniel



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