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    SubjectRe: [PATCH 2/3] scsi: add hooks for host runtime power management
    On Wed, 2 Nov 2011, Lin Ming wrote:

    > Adds ->suspend and ->resume callbacks in struct scsi_host_template
    > to do host runtime power management.
    >
    > Signed-off-by: Lin Ming <ming.m.lin@intel.com>
    > ---
    > drivers/scsi/scsi_pm.c | 34 +++++++++++++++++++++++++++++++---
    > include/scsi/scsi_host.h | 8 ++++++++
    > 2 files changed, 39 insertions(+), 3 deletions(-)
    >
    > diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
    > index 1be6c5a..5742bed2 100644
    > --- a/drivers/scsi/scsi_pm.c
    > +++ b/drivers/scsi/scsi_pm.c
    > @@ -42,6 +42,28 @@ static int scsi_dev_type_resume(struct device *dev)
    > return err;
    > }
    >
    > +static int scsi_host_suspend(struct device *dev)
    > +{
    > + struct Scsi_Host *shost = dev_to_shost(dev);
    > + int err = 0;
    > +
    > + if (shost->hostt->suspend)
    > + err = shost->hostt->suspend(shost);
    > +
    > + return err;
    > +}
    > +
    > +static int scsi_host_resume(struct device *dev)
    > +{
    > + struct Scsi_Host *shost = dev_to_shost(dev);
    > + int err = 0;
    > +
    > + if (shost->hostt->resume)
    > + err = shost->hostt->resume(shost);
    > +
    > + return err;
    > +}

    These don't need to be independent routines. You can put them inline
    in scsi_runtime_suspend() and scsi_runtime_resume() below; that's how
    the device code is written.

    > @@ -132,7 +160,7 @@ static int scsi_runtime_idle(struct device *dev)
    >
    > /* Insert hooks here for targets, hosts, and transport classes */
    >
    > - if (scsi_is_sdev_device(dev))
    > + if (scsi_is_sdev_device(dev) || scsi_is_host_device(dev))
    > err = pm_schedule_suspend(dev, 100);

    This is wrong. The 100-ms delay is meant for devices only. There's
    no reason to delay suspending a host once everything beneath it is
    suspended. Just leave the code the way it is now.

    > else
    > err = pm_runtime_suspend(dev);
    > diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
    > index f1f2644..512e2a0 100644
    > --- a/include/scsi/scsi_host.h
    > +++ b/include/scsi/scsi_host.h
    > @@ -356,6 +356,14 @@ struct scsi_host_template {
    > enum blk_eh_timer_return (*eh_timed_out)(struct scsi_cmnd *);
    >
    > /*
    > + * Optional routine for scsi host runtime pm.
    > + *
    > + * Status: OPTIONAL
    > + */
    > + int (*suspend)(struct Scsi_Host *);
    > + int (*resume)(struct Scsi_Host *);

    The comment should explain what drivers are supposed to do when these
    hooks are called. In particular, the suspend callback should _not_
    power-down the entire host adapter; it should power-down only the
    circuitry that controls the interface to the SCSI bus. The upstream
    interface to the CPU should remain at full power.

    If there's no way to power-down just that part of the host adapter then
    there's no need to have these callbacks at all. The low-level driver
    can simply use the runtime PM API on its own struct device.

    Alan Stern



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