linux-kernel - Re: [PATCH v2 4/4] ata: add ata port runtime PM callbacks

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Date:	Wed, 16 Nov 2011 21:14:12 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Tejun Heo <tj@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <JBottomley@...allels.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	"Zhang, Rui" <rui.zhang@...el.com>
Subject: Re: [PATCH v2 4/4] ata: add ata port runtime PM callbacks

On Wed, 2011-11-16 at 00:08 +0800, Alan Stern wrote:
> On Tue, 15 Nov 2011, Tejun Heo wrote:
> 
> > On Tue, Nov 15, 2011 at 04:51:29PM +0800, Lin Ming wrote:
> > > > This is not the right approach.  You should look instead at 
> > > > scsi_dev_type_suspend() in scsi_pm.c.  If the device is already runtime 
> > > > suspended then the routine should return immediately.
> > > 
> > > How about below?
> > > 
> > > diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
> > > index d329f8b..94b60bd 100644
> > > --- a/drivers/scsi/scsi_pm.c
> > > +++ b/drivers/scsi/scsi_pm.c
> > > @@ -20,6 +20,9 @@ static int scsi_dev_type_suspend(struct device *dev, pm_message_t msg)
> > >  	struct device_driver *drv;
> > >  	int err;
> > >  
> > > +	if (pm_runtime_suspended(dev))
> > > +		return 0;
> > > +
> > 
> > Something to be careful about is there are different types of suspend
> > states (PMSG_*).  IIUC, runtime PM is using PMSG_SUSPEND.  Other
> > states may or may not be compatible with PMSG_SUSPEND expectations, so
> > you can skip suspend operation if the newly requested state is
> > PMSG_SUSPEND but otherwise the controller needs to be woken up and
> > told to comply to the new state.
> 
> That's right.  Surprisingly enough (and contrary to what I wrote
> earlier), the sd_suspend() routine doesn't spin down a drive for
> runtime suspend.  This probably should be considered a bug.
> 
> Anyway, it looks like the correct approach would be more like this:

Thanks.

I think ata_port_suspend also needs to call pm_runtime_resume, as below.

static int ata_port_suspend(struct device *dev)
{
        struct ata_port *ap = to_ata_port(dev);
        int rc;

        pm_runtime_resume(dev);
        rc = ata_port_request_pm(ap, PMSG_SUSPEND, 0, ATA_EHI_QUIET, 1);
        return rc;
}

> 
>  static int scsi_bus_suspend_common(struct device *dev, pm_message_t msg)
>  {
>  	int err = 0;
>  
> -	if (scsi_is_sdev_device(dev))
> +	if (scsi_is_sdev_device(dev)) {
>  		pm_runtime_resume(dev);
>  		err = scsi_dev_type_suspend(dev, msg);
> +	}
>  	return err;
>  }
> 
> Alan Stern
> 


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