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

Martin Kepplinger
2020-07-29T16:44:28Z

Am 29. Juli 2020 17:44:42 MESZ schrieb James Bottomley <James.Bottomley@HansenPartnership.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
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