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

James Bottomley
2020-07-29T15:44:50Z

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