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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Alan Stern <stern@rowland.harvard.edu>,
	Martin Kepplinger <martin.kepplinger@puri.sm>
Cc: Bart Van Assche <bvanassche@acm.org>,
	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: Wed, 29 Jul 2020 11:29:09 -0700
Message-ID: <1596047349.4356.84.camel@HansenPartnership.com> (raw)
In-Reply-To: <20200729182515.GB1580638@rowland.harvard.edu>

On Wed, 2020-07-29 at 14:25 -0400, Alan Stern wrote:
> On Wed, Jul 29, 2020 at 06:43:48PM +0200, Martin Kepplinger wrote:
[...]
> > > > --- a/drivers/scsi/scsi_error.c
> > > > +++ b/drivers/scsi/scsi_error.c
> > > > @@ -554,16 +554,8 @@ int scsi_check_sense(struct scsi_cmnd
> > > > *scmd)
> > > >                  * so that we can deal with it there.
> > > >                  */
> > > >                 if (scmd->device->expecting_cc_ua) {
> > > > -                       /*
> > > > -                        * Because some device does not queue
> > > > unit
> > > > -                        * attentions correctly, we carefully
> > > > check
> > > > -                        * additional sense code and qualifier
> > > > so as
> > > > -                        * not to squash media change unit
> > > > attention.
> > > > -                        */
> > > > -                       if (sshdr.asc != 0x28 || sshdr.ascq !=
> > > > 0x00)
> > > > {
> > > > -                               scmd->device->expecting_cc_ua =
> > > > 0;
> > > > -                               return NEEDS_RETRY;
> > > > -                       }
> > > > +                       scmd->device->expecting_cc_ua = 0;
> > > > +                       return NEEDS_RETRY;
> > > 
> > > Well, yes, but you can't do this because it would lose us media
> > > change events in the non-suspend/resume case which we really
> > > don't want.  That's why I was suggesting a new flag.
> > > 
> > > James
> > 
> > also if I set expecting_cc_ua in resume() only, like I did?
> 
> That wouldn't make any difference.  The information sent by your
> card reader has sshdr.asc == 0x28 and sshdr.ascq == 0x00 (you can see
> it in the log).  So because of the code here in scsi_check_sense(),
> which you can't change, the Unit Attention sent by the card reader
> would not be  retried even if you do set the flag in resume().

But if we had a new flag, like expecting_media_change, you could set
that in resume and we could condition the above test in the code on it
and reset it and do a retry if it gets set.  I'm not saying we have to
do it this way, but it sounds like we have to do something in the
kernel, so I think the flag will become necessary but there might be a
bit of policy based dance around how it gets set in the kernel (to
avoid losing accurate media change events).

James


  reply index

Thread overview: 68+ 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
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 [this message]
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
2020-08-23 14:57                                                                         ` [PATCH] block: Fix bug in runtime-resume handling Alan Stern
2020-08-24 17:48                                                                           ` Bart Van Assche
2020-08-24 20:13                                                                             ` Alan Stern
2020-08-26  7:48                                                                               ` Martin Kepplinger
2020-08-27 17:42                                                                                 ` Martin Kepplinger
2020-08-27 20:29                                                                                   ` Alan Stern
2020-08-29  7:24                                                                                     ` Martin Kepplinger
2020-08-29 15:26                                                                                       ` Alan Stern
2020-08-29 16:33                                                                                         ` Martin Kepplinger
2020-08-29 18:56                                                                                           ` Alan Stern
2020-08-30  0:38                                                                                             ` Bart Van Assche
2020-08-30  1:06                                                                                               ` Alan Stern
2020-07-29 15:40                                       ` [PATCH] scsi: sd: add runtime pm to open / release 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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