[3/7] scsi: Drop runtime PM usage count after host is added

Runtime PM of the SCSI host is already handled by calls to
scsi_autopm_get_host() and scsi_autopm_put_host() from appropriate places
whenever the host needs to be powered on. This works fine when there is
device connected to the host as once it runtime suspends the host will too.

However, if there is no device connected the host is never runtime
suspended (the usage counter is always 0).

Allow runtime suspend of host even if it has no devices connected by
calling scsi_autopm_put_host() at the end of scsi_add_host_with_dma(). We
temporarily increase runtime PM usage counter first so call to
scsi_autopm_put_host() will result idle request to be scheduled for the
device.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
 drivers/scsi/hosts.c | 7 +++++++
 1 file changed, 7 insertions(+)

Hi Mika,

On Thu, Feb 18, 2016 at 7:54 PM, Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
> Runtime PM of the SCSI host is already handled by calls to
> scsi_autopm_get_host() and scsi_autopm_put_host() from appropriate places
> whenever the host needs to be powered on. This works fine when there is
> device connected to the host as once it runtime suspends the host will too.
>
> However, if there is no device connected the host is never runtime
> suspended (the usage counter is always 0).
>
> Allow runtime suspend of host even if it has no devices connected by
> calling scsi_autopm_put_host() at the end of scsi_add_host_with_dma(). We
> temporarily increase runtime PM usage counter first so call to
> scsi_autopm_put_host() will result idle request to be scheduled for the
> device.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/scsi/hosts.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index 82ac1cd818ac..e46bf4d152a0 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -250,6 +250,12 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>         if (error)
>                 goto out_destroy_freelist;
>
> +       /*
> +        * Increase usage count temporarily here so that calling
> +        * scsi_autopm_put_host() will trigger runtime idle if there is
> +        * nothing else preventing suspending the device.
> +        */
> +       pm_runtime_get_noresume(&shost->shost_gendev);
>         pm_runtime_set_active(&shost->shost_gendev);
>         pm_runtime_enable(&shost->shost_gendev);
>         device_enable_async_suspend(&shost->shost_gendev);
> @@ -290,6 +296,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>                 goto out_destroy_host;
>
>         scsi_proc_host_add(shost);
> +       scsi_autopm_put_host(shost);

Would it be cleaner to export the code that runs when the usage
counter decrements and call it here?

Thanks,

On Fri, Feb 19, 2016 at 09:50:50AM +1100, Julian Calaby wrote:
> Hi Mika,
> 
> On Thu, Feb 18, 2016 at 7:54 PM, Mika Westerberg
> <mika.westerberg@linux.intel.com> wrote:
> > Runtime PM of the SCSI host is already handled by calls to
> > scsi_autopm_get_host() and scsi_autopm_put_host() from appropriate places
> > whenever the host needs to be powered on. This works fine when there is
> > device connected to the host as once it runtime suspends the host will too.
> >
> > However, if there is no device connected the host is never runtime
> > suspended (the usage counter is always 0).
> >
> > Allow runtime suspend of host even if it has no devices connected by
> > calling scsi_autopm_put_host() at the end of scsi_add_host_with_dma(). We
> > temporarily increase runtime PM usage counter first so call to
> > scsi_autopm_put_host() will result idle request to be scheduled for the
> > device.
> >
> > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > ---
> >  drivers/scsi/hosts.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> > index 82ac1cd818ac..e46bf4d152a0 100644
> > --- a/drivers/scsi/hosts.c
> > +++ b/drivers/scsi/hosts.c
> > @@ -250,6 +250,12 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
> >         if (error)
> >                 goto out_destroy_freelist;
> >
> > +       /*
> > +        * Increase usage count temporarily here so that calling
> > +        * scsi_autopm_put_host() will trigger runtime idle if there is
> > +        * nothing else preventing suspending the device.
> > +        */
> > +       pm_runtime_get_noresume(&shost->shost_gendev);
> >         pm_runtime_set_active(&shost->shost_gendev);
> >         pm_runtime_enable(&shost->shost_gendev);
> >         device_enable_async_suspend(&shost->shost_gendev);
> > @@ -290,6 +296,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
> >                 goto out_destroy_host;
> >
> >         scsi_proc_host_add(shost);
> > +       scsi_autopm_put_host(shost);
> 
> Would it be cleaner to export the code that runs when the usage
> counter decrements and call it here?

There actually is no code to run. This just ensures that the device
runtime_idle gets called which allows the parent device to runtime
suspend (as it returns 0). Alternative way would be just to call
pm_request_idle() directly here.
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