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

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Date:   Wed, 29 Jul 2020 18:43:48 +0200
From:   Martin Kepplinger <martin.kepplinger@...i.sm>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Alan Stern <stern@...land.harvard.edu>
CC:     Bart Van Assche <bvanassche@....org>,
        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



Am 29. Juli 2020 17:44:42 MESZ schrieb James Bottomley <James.Bottomley@...senPartnership.com>:
>On Wed, 2020-07-29 at 17:40 +0200, Martin Kepplinger wrote:
>> On 29.07.20 16:53, James Bottomley wrote:
>> > On Wed, 2020-07-29 at 07:46 -0700, James Bottomley wrote:
>> > > On Wed, 2020-07-29 at 10:32 -0400, Alan Stern wrote:
>[...]
>> > > > This error report comes from the SCSI layer, not the block
>> > > > layer.
>> > > 
>> > > That sense code means "NOT READY TO READY CHANGE, MEDIUM MAY HAVE
>> > > CHANGED" so it sounds like it something we should be
>> > > ignoring.  Usually this signals a problem, like you changed the
>> > > medium manually (ejected the CD).  But in this case you can tell
>> > > us to expect this by setting
>> > > 
>> > > sdev->expecting_cc_ua
>> > > 
>> > > And we'll retry.  I think you need to set this on all resumed
>> > > devices.
>> > 
>> > Actually, it's not quite that easy, we filter out this ASC/ASCQ
>> > combination from the check because we should never ignore medium
>> > might have changed events on running devices.  We could ignore it
>> > if we had a flag to say the power has been yanked (perhaps an
>> > additional sdev flag you set on resume) but we would still miss the
>> > case where you really had powered off the drive and then changed
>> > the media ... if you can regard this as the user's problem, then we
>> > might have a solution.
>> > 
>> > James
>> >  
>> 
>> oh I see what you mean now, thanks for the ellaboration.
>> 
>> if I do the following change, things all look normal and runtime pm
>> works. I'm not 100% sure if just setting expecting_cc_ua in resume()
>> is "correct" but that looks like it is what you're talking about:
>> 
>> (note that this is of course with the one block layer diff applied
>> that Alan posted a few emails back)
>> 
>> 
>> --- 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?

-- 
Martin Kepplinger
xmpp: martink@...ber.at
Sent from mobile.