Re: [PATCH RFC v2 1/1] scsi: pm: Leave runtime PM status alone during system resume/thaw/restore

[Can Guo]

Hi Alan,

On 2020-11-21 00:35, Alan Stern wrote:
> On Fri, Nov 20, 2020 at 12:37:22AM -0800, Can Guo wrote:
> > Runtime resume is handled by runtime PM framework, no need to forcibly
> > set runtime PM status to RPM_ACTIVE during system resume/thaw/restore.
>
> Sorry, I don't understand this explanation at all.
>
> Sure, runtime resume is handled by the runtime PM framework.  But this
> patch changes the code for system resume, which is completely 
> different.
>
> Following a system resume, the hardware will be at full power.  We 
> don't
> want the kernel to think that the device is still in runtime suspend;
> otherwise is would never put the device back into low-power mode.

How about adding below lines to the patch?

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index 908f27f..7ebe582 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -75,9 +75,11 @@ static int scsi_dev_type_resume(struct device *dev,
        const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : 
NULL;
        int err = 0;

-       err = cb(dev, pm);
-       scsi_device_resume(to_scsi_device(dev));
-       dev_dbg(dev, "scsi resume: %d\n", err);
+       if (pm_runtime_active(dev)) {
+               err = cb(dev, pm);
+               scsi_device_resume(to_scsi_device(dev));
+               dev_dbg(dev, "scsi resume: %d\n", err);
+       }

        return err;
 }

Whenever a device is accessed, the issuer or somewhere in the path
should do something like pm_runtime_get_sync (e.g. in sg_open()) or
pm_runtime_resume() (e.g. in blk_queue_enter()), in either sync or
async way. After the job (read/write/ioctl or whatever) is done,
either a pm_runtime_put_sync() or auto runtime suspend puts the device
back into runtime suspended/low-power mode. Since the func
scsi_bus_suspend_common() does nothing if device is already in runtime
suspended mode, scsi_dev_type_resume() should only resume the device
if it is runtime active.

Thanks,

Can Guo.

> Alan Stern
>
> > Cc: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
> > Cc: Bart Van Assche <bvanassche@xxxxxxx>
> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Can Guo <cang@xxxxxxxxxxxxxx>
> > ---
> >
> > Changes since v1:
> > - Incorporated Bart's comments
> >
> > ---
> >  drivers/scsi/scsi_pm.c | 24 +-----------------------
> >  1 file changed, 1 insertion(+), 23 deletions(-)
> >
> > diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
> > index 3717eea..908f27f 100644
> > --- a/drivers/scsi/scsi_pm.c
> > +++ b/drivers/scsi/scsi_pm.c
> > @@ -79,25 +79,6 @@ static int scsi_dev_type_resume(struct device *dev,
> >  	scsi_device_resume(to_scsi_device(dev));
> >  	dev_dbg(dev, "scsi resume: %d\n", err);
> >
> > -	if (err == 0) {
> > -		pm_runtime_disable(dev);
> > -		err = pm_runtime_set_active(dev);
> > -		pm_runtime_enable(dev);
> > -
> > -		/*
> > -		 * Forcibly set runtime PM status of request queue to "active"
> > -		 * to make sure we can again get requests from the queue
> > -		 * (see also blk_pm_peek_request()).
> > -		 *
> > -		 * The resume hook will correct runtime PM status of the disk.
> > -		 */
> > -		if (!err && scsi_is_sdev_device(dev)) {
> > -			struct scsi_device *sdev = to_scsi_device(dev);
> > -
> > -			blk_set_runtime_active(sdev->request_queue);
> > -		}
> > -	}
> > -
> >  	return err;
> >  }
> >
> > @@ -165,11 +146,8 @@ static int scsi_bus_resume_common(struct device 
> > *dev,
> >  		 */
> >  		if (strncmp(scsi_scan_type, "async", 5) != 0)
> >  			async_synchronize_full_domain(&scsi_sd_pm_domain);
> > -	} else {
> > -		pm_runtime_disable(dev);
> > -		pm_runtime_set_active(dev);
> > -		pm_runtime_enable(dev);
> >  	}
> > +
> >  	return 0;
> >  }
> >
> > --
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
> > Linux Foundation Collaborative Project.