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    SubjectRe: [RFC 0/5] scsi, sd, pm, request based runtime PM for scsi disk
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    Hi, Alan,

    On Mon, 2012-02-06 at 10:13 -0500, Alan Stern wrote:
    > On Mon, 6 Feb 2012, Huang Ying wrote:
    >
    > > SSD becomes more and more popular, this makes it possible to put disk into
    > > low power state more often. And request based runtime PM for scsi disk is
    > > more useful than open/close based one because disk is normally mounted at
    > > most time.
    > >
    > > One known issue, because SCSI TEST_UNIT_READY will be put into request
    > > queue every 2 seconds by default, this makes it hard for disk to sleep.
    > > Maybe we can implement check_events callback in some other way?
    > >
    > > [RFC 1/5] pm, runtime, Add resume notifier
    > > [RFC 2/5] scsi, pm, rename scsi_autopm_get/put_xxx to
    > > [RFC 3/5] scsi, pm, add pm_runtime_get/put in scsi request
    > > [RFC 4/5] scsi, pm, use autosuspend for scsi runtime PM
    > > [RFC 5/5] scsi, sd, pm, request based runtime PM support
    >
    > Your whole approach is at the wrong level. Runtime PM between I/O
    > requests for block devices should be implemented in the block layer,
    > not in the SCSI layer.
    >
    > It also is much more difficult than your patches would indicate. For
    > example, some USB card readers indicate a media change every time they
    > resume; therefore they must not be suspended while the device file is
    > open.
    >
    > Another difficulty arises because some drivers need to send SCSI
    > commands (such as SYNCHRONIZE CACHE) _while_ suspending or resuming.

    Thank you very much for your valuable response! We will do more
    research work on this topic, including your previous effort. :)

    Best Regards,
    Huang Ying




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