Re: [PATCH v6 1/7] scsi: sr: support runtime pm for ODD

From: Oliver Neukum <oliver@neukum.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Aaron Lu <aaron.lwe@gmail.com>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	Jeff Garzik <jgarzik@pobox.com>,
	linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-acpi@vger.kernel.org,
	Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH v6 1/7] scsi: sr: support runtime pm for ODD
Date: Thu, 06 Sep 2012 17:25:20 +0200	[thread overview]
Message-ID: <6471150.bvyUxmYfmp@linux-lqwf.site> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1209061103530.1363-100000@iolanthe.rowland.org>

On Thursday 06 September 2012 11:06:49 Alan Stern wrote:
> On Thu, 6 Sep 2012, Aaron Lu wrote:
> 
> > > That's why we have an autosuspend delay.  Although for some reason the 
> > > SCSI subsystem doesn't use it currently...  We need to add a call to 
> > > pm_runtime_use_autosuspend() in scsi_sysfs_add_sdev().  Likewise, the 
> > > pm_schedule_suspend() call in scsi_runtime_idle() should be changed to 
> > > pm_runtime_autosuspend().  And there should be calls to 
> > > pm_runtime_set_autosuspend_delay() in the sd and sr drivers.
> > 
> > I tried to use autosuspend when preparing the patch, but the fact that
> > the devices will be polled every 2 seconds make it impossible to enter
> > suspend state if the autosuspend delay is larger than that.
> 
> You can always increase the polling interval.
> 
> But in the long run that wouldn't be a good solution.  What I'd really 
> like is a way to do the status polling without having it reset the 
> idle timer.
> 
> Oliver, what do you think?  Would that be a good solution?

Well, we could introduce a flag into the requests for the polls.
But best would be to simply declare a device immediately idle
as soon as we learn that it has no medium. No special casing
would be needed.

	Regards
		Oliver