linux-kernel - Re: [PATCH] scsi: sd: add runtime pm to open / release

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Date:   Sun, 28 Jun 2020 09:10:56 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Martin Kepplinger <martin.kepplinger@...i.sm>, jejb@...ux.ibm.com,
        Can Guo <cang@...eaurora.org>, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...i.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release

On Sat, Jun 27, 2020 at 07:37:54PM -0700, Bart Van Assche wrote:
> On 2020-06-26 08:44, Alan Stern wrote:
> > On Fri, Jun 26, 2020 at 08:07:51AM -0700, Bart Van Assche wrote:
> >> As far as I know runtime power management support in the sd driver is working
> >> fine and is being used intensively by the UFS driver. The following commit was
> >> submitted to fix a bug encountered by an UFS developer: 05d18ae1cc8a ("scsi:
> >> pm: Balance pm_only counter of request queue during system resume") # v5.7.
> > 
> > I just looked at that commit for the first time.
> > 
> > Instead of making the SCSI driver do the work of deciding what routine to 
> > call, why not redefine blk_set_runtime_active(q) to simply call 
> > blk_post_runtime_resume(q, 0)?  Or vice versa: if err == 0 have 
> > blk_post_runtime_resume call blk_set_runtime_active?
> > 
> > After all, the two routines do almost the same thing -- and the bug 
> > addressed by this commit was caused by the difference in their behaviors.
> > 
> > If the device was already runtime-active during the system suspend, doing 
> > an extra clear of the pm_only counter won't hurt anything.
> 
> Hi Alan,
> 
> Do you want to submit a patch that implements this change or do you
> perhaps expect me to do that?

I'll submit a patch in a few days.  I just wanted to check first that the 
idea was sound.

Alan Stern