Re: [PATCH v7 2/6] scsi: sr: support runtime pm

[Aaron Lu <aaron.lu@intel.com>]

On Thu, Sep 20, 2012 at 10:48:10PM +0200, Rafael J. Wysocki wrote:
> On Wednesday, September 12, 2012, Aaron Lu wrote:
> > Place the ODD into runtime suspend state as soon as there is nobody
> > using it.
> 
> OK, so how is ODD related to the sr driver?

As Alan has explained, ODD(optical disk drive) is driven by scsi
sr driver.

> 
> > The only exception is, if we just find that a new medium is
> > inserted, we wait for the next events checking to idle it.
> 
> What exactly do you mean by "to idle it"?

I mean to put its usage count so that its idle callback will kick in.

> 
> Does this patch have any functional effect without the following patches?

Yes, this one alone takes care of ODD's runtime pm while the following
patches take care of removing its power after it's runtime suspended.
But it doesn't have any real benefit without the following patches.

> 
> > Based on ideas of Alan Stern and Oliver Neukum.
> > 
> > Signed-off-by: Aaron Lu <aaron.lu@intel.com>
> > ---
> >  drivers/scsi/sr.c | 29 +++++++++++++++++++++++++----
> >  1 file changed, 25 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
> > index 5fc97d2..7a8222f 100644
> > --- a/drivers/scsi/sr.c
> > +++ b/drivers/scsi/sr.c
> > @@ -45,6 +45,7 @@
> >  #include <linux/blkdev.h>
> >  #include <linux/mutex.h>
> >  #include <linux/slab.h>
> > +#include <linux/pm_runtime.h>
> >  #include <asm/uaccess.h>
> >  
> >  #include <scsi/scsi.h>
> > @@ -146,8 +147,12 @@ static inline struct scsi_cd *scsi_cd_get(struct gendisk *disk)
> >  	kref_get(&cd->kref);
> >  	if (scsi_device_get(cd->device))
> >  		goto out_put;
> > +	if (scsi_autopm_get_device(cd->device))
> > +		goto out_pm;
> >  	goto out;
> 
> Why don't you do
> 
> > +	if (!scsi_autopm_get_device(cd->device))
> > +		goto out;
> 
> without the new label?

I was just stupidly following the pattern.
Thanks and I'll change this.

> 
> >  
> > + out_pm:
> > +	scsi_device_put(cd->device);
> >   out_put:
> >  	kref_put(&cd->kref, sr_kref_release);
> >  	cd = NULL;
> > @@ -163,6 +168,7 @@ static void scsi_cd_put(struct scsi_cd *cd)
> >  	mutex_lock(&sr_ref_mutex);
> >  	kref_put(&cd->kref, sr_kref_release);
> >  	scsi_device_put(sdev);
> > +	scsi_autopm_put_device(sdev);
> >  	mutex_unlock(&sr_ref_mutex);
> >  }
> >  
> > @@ -211,7 +217,7 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi,
> >  				    unsigned int clearing, int slot)
> >  {
> >  	struct scsi_cd *cd = cdi->handle;
> > -	bool last_present;
> > +	bool last_present = cd->media_present;
> >  	struct scsi_sense_hdr sshdr;
> >  	unsigned int events;
> >  	int ret;
> > @@ -220,6 +226,8 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi,
> >  	if (CDSL_CURRENT != slot)
> >  		return 0;
> >  
> > +	scsi_autopm_get_device(cd->device);
> > +
> >  	events = sr_get_events(cd->device);
> >  	cd->get_event_changed |= events & DISK_EVENT_MEDIA_CHANGE;
> >  
> > @@ -246,10 +254,9 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi,
> >  	}
> >  
> >  	if (!(clearing & DISK_EVENT_MEDIA_CHANGE))
> > -		return events;
> > +		goto out;
> >  do_tur:
> >  	/* let's see whether the media is there with TUR */
> > -	last_present = cd->media_present;
> >  	ret = scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr);
> >  
> >  	/*
> > @@ -270,7 +277,7 @@ do_tur:
> >  	}
> >  
> >  	if (cd->ignore_get_event)
> > -		return events;
> > +		goto out;
> >  
> >  	/* check whether GET_EVENT is reporting spurious MEDIA_CHANGE */
> >  	if (!cd->tur_changed) {
> > @@ -287,6 +294,12 @@ do_tur:
> >  	cd->tur_changed = false;
> >  	cd->get_event_changed = false;
> >  
> > +out:
> > +	if (cd->media_present && !last_present)
> > +		pm_runtime_put_noidle(&cd->device->sdev_gendev);
> > +	else
> > +		scsi_autopm_put_device(cd->device);
> > +
> 
> This thing is asking for a comment.
> 
> It looks like you're kind of avoiding to call _idle() for the device, but why?
> What might go wrong if pm_runtime_put() is used instead of the whole conditional,
> among other things?

The above code means, if we found that a disc is just inserted(reflected
by cd->media_present is true and last_present is false), we do not want
to put the device into suspend state immediately until next poll. In the
interval, some programs may decide to use this device by opening it.

Nothing will go wrong, but it can possibly avoid a runtime status change.

> 
> >  	return events;
> >  }
> >  
> > @@ -715,9 +728,14 @@ static int sr_probe(struct device *dev)
> >  	dev_set_drvdata(dev, cd);
> >  	disk->flags |= GENHD_FL_REMOVABLE;
> >  	add_disk(disk);
> > +	disk_events_set_poll_msecs(disk, 5000);
> 
> Why do you need this and why is the poll interval universally suitable?

For a system with udev, the block module parameter events_dfl_poll_msecs
will be set to 2s. If disk's events_poll_msecs is not set, that will be
used. So the disk will be polled every 2s, that means it will be runtime
suspended/resumed every 2s if there is no user. I set it to 5s so that
the device can stay in runtime suspended state longer.

And the sysfs interface is still there, if udev thinks a device needs
special setting, it will do that and I'll not overwrite that setting.

> 
> >  
> >  	sdev_printk(KERN_DEBUG, sdev,
> >  		    "Attached scsi CD-ROM %s\n", cd->cdi.name);
> > +
> > +	/* enable runtime pm */
> 
> Not really.  What it does is to enable the device to be suspended.

OK, will change this.

> 
> > +	scsi_autopm_put_device(cd->device);
> > +
> >  	return 0;
> >  
> >  fail_put:
> > @@ -965,6 +983,9 @@ static int sr_remove(struct device *dev)
> >  {
> >  	struct scsi_cd *cd = dev_get_drvdata(dev);
> >  
> > +	/* disable runtime pm */
> 
> And that prevents the device from being suspended (which means that it's
> going to be resumed at this point in case it was suspended before).

Yes, that's what I want.
We are removing its driver and I think we should undo what we have done
to it.

Thanks,
Aaron
> 
> > +	scsi_autopm_get_device(cd->device);
> > +
> >  	blk_queue_prep_rq(cd->device->request_queue, scsi_prep_fn);
> >  	del_gendisk(cd->disk);
> >  
> > 
> 
> Thanks,
> Rafael