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From: Alan Stern <stern@rowland.harvard.edu>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Martin Kepplinger <martin.kepplinger@puri.sm>,
	jejb@linux.ibm.com, Can Guo <cang@codeaurora.org>,
	martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel@puri.sm
Subject: Re: [PATCH] scsi: sd: add runtime pm to open / release
Date: Fri, 26 Jun 2020 11:44:41 -0400
Message-ID: <20200626154441.GA296771@rowland.harvard.edu> (raw)
In-Reply-To: <1379e21d-c51a-3710-e185-c2d7a9681fb7@acm.org>

On Fri, Jun 26, 2020 at 08:07:51AM -0700, Bart Van Assche wrote:
> On 2020-06-25 01:16, Martin Kepplinger wrote:
> > here's roughly what happens when enabling runtime PM in sysfs (again,
> > because sd_probe() calls autopm_put() and thus allows it:
> > 
> > [   27.384446] sd 0:0:0:0: scsi_runtime_suspend
> > [   27.432282] blk_pre_runtime_suspend
> > [   27.435783] sd_suspend_common
> > [   27.438782] blk_post_runtime_suspend
> > [   27.442427] scsi target0:0:0: scsi_runtime_suspend
> > [   27.447303] scsi host0: scsi_runtime_suspend
> > 
> > then I "mount /dev/sda1 /mnt" and none of the resume() functions get
> > called. To me it looks like the sd driver should initiate resuming, and
> > that's not implemented.
> > 
> > what am I doing wrong or overlooking? how exactly does (or should) the
> > block layer initiate resume here?
> 
> 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.

> I'm not sure which bug is causing trouble on your setup but I think it's likely
> that the root cause is somewhere else than in the block layer, the SCSI core
> or the SCSI sd driver.
> 
> Bart.

Martin's best approach would be to add some debugging code to find out why 
blk_queue_enter() isn't calling bkl_pm_request_resume(), or why that call 
doesn't lead to pm_request_resume().

Alan Stern

  reply index

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-23 11:10 Martin Kepplinger
2020-06-24 13:33 ` Bart Van Assche
2020-06-25  8:16   ` Martin Kepplinger
2020-06-25 14:52     ` Alan Stern
2020-06-26  3:53     ` Bart Van Assche
2020-06-26 15:07     ` Bart Van Assche
2020-06-26 15:44       ` Alan Stern [this message]
2020-06-28  2:37         ` Bart Van Assche
2020-06-28 13:10           ` Alan Stern
2020-06-29  9:42         ` Martin Kepplinger
2020-06-29 16:15           ` Alan Stern
2020-06-29 16:56             ` Bart Van Assche
2020-06-29 17:40               ` Alan Stern
2020-06-30  3:33             ` Martin Kepplinger
2020-06-30 13:38               ` Alan Stern
2020-06-30 15:59             ` Bart Van Assche
2020-06-30 18:02               ` Alan Stern
2020-06-30 19:23                 ` Bart Van Assche
2020-06-30 19:38                   ` Alan Stern
2020-06-30 23:31                     ` Bart Van Assche
2020-07-01  0:49                       ` Alan Stern
2020-07-06 16:41                         ` Alan Stern
2020-07-28  7:02                           ` Martin Kepplinger
2020-07-28 20:02                             ` Alan Stern
2020-07-29 14:12                               ` Martin Kepplinger
2020-07-29 14:32                                 ` Alan Stern
2020-07-29 14:44                                   ` Martin K. Petersen
2020-07-29 14:56                                     ` Alan Stern
2020-07-29 14:46                                   ` James Bottomley
2020-07-29 14:53                                     ` James Bottomley
2020-07-29 15:40                                       ` Martin Kepplinger
2020-07-29 15:44                                         ` James Bottomley
2020-07-29 16:43                                           ` Martin Kepplinger
2020-07-29 18:25                                             ` Alan Stern
2020-07-29 18:29                                               ` James Bottomley
2020-07-30  8:52                                                 ` Martin Kepplinger
2020-07-30  8:54                                                   ` Martin Kepplinger
2020-07-30 15:10                                                   ` Alan Stern
2020-08-04  9:39                                                     ` Martin Kepplinger
2020-08-07  9:51                                                       ` Martin Kepplinger
2020-08-07 14:30                                                         ` Alan Stern
2020-08-08  6:59                                                           ` Martin Kepplinger
2020-08-08 15:05                                                             ` Alan Stern
2020-08-09  9:20                                                               ` Martin Kepplinger
2020-08-09 15:26                                                                 ` Alan Stern
2020-08-10 12:03                                                                   ` Martin Kepplinger
2020-08-10 14:13                                                                     ` Alan Stern
2020-08-11  7:55                                                                       ` Martin Kepplinger
2020-08-11 13:48                                                                         ` Alan Stern
2020-07-29 15:40                                       ` Alan Stern
2020-07-29 15:49                                         ` James Bottomley
2020-07-29 16:17                                           ` Alan Stern
2020-07-29 15:52                                         ` Martin Kepplinger
2020-07-29 18:10                                   ` Douglas Gilbert
2020-07-30  8:05             ` Martin Kepplinger
2020-07-30 15:14               ` Alan Stern

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