linux-kernel - Re: [RFC PATCH v3 3/4] block: implement runtime pm strategy

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Message-ID: <Pine.LNX.4.44L0.1205231052270.1566-100000@iolanthe.rowland.org>
Date:	Wed, 23 May 2012 10:53:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lin Ming <ming.m.lin@...el.com>
cc:	Jens Axboe <axboe@...nel.dk>, <linux-kernel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-scsi@...r.kernel.org>
Subject: Re: [RFC PATCH v3 3/4] block: implement runtime pm strategy

On Wed, 23 May 2012, Lin Ming wrote:

> >> +             /* Only PM request is allowed to go if the queue is suspended */
> >> +             if (q->rpm_status != RPM_ACTIVE && !(rq->cmd_flags & REQ_PM)) {
> >> +                     rq = NULL;
> >> +                     break;
> >> +             }
> >
> > Not even PM requests should be allowed to go if the status is
> > RPM_SUSPENDED.
> 
> PM requests are used to wake up the device.
> If they are not allowed to go, then how to wake up the device?

When blk_pre_runtime_resume runs, the status is changed to
RPM_RESUMING.  _Then_ PM requests are allowed to go.  Not before.

Alan Stern

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