Re: [qemu-s390x] [RFC 15/15] s390-bios: Use sense ccw to ensure consistent device state at boot time

[Jason J. Herne]

On 07/06/2018 06:08 AM, Cornelia Huck wrote:
> On Thu,  5 Jul 2018 13:25:43 -0400
> "Jason J. Herne" <address@hidden> wrote:
>
> > If a vfio-ccw device is left in an error state (example: pending unit
> > check) then it is possible for that state to persist for a vfio-ccw device even
> > after the enable subchannel that we do to bring the device online. If this state
> > is allowed to persist then even simple I/O operations will needlessly fail. A
> > basic sense ccw is used to clear this error state for the boot device.
>
> Another thing: What about unsolicited interrupts? I.e., you enable the
> subchannel, and then it becomes pending with unsolicited status. Do you
> have any handling for that (or plan to add it)?
>
> We could ignore that for virtio devices, but probably not for dasds.
...
> Hmm. Could an error condition reassert itself after it was cleared?
> Probably not worth spending too much time on, though.
>
> > +
> >       switch (cu_type(blk_schid)) {
> >       case 0x3990:  /* Real DASD device */
> >           dasd_ipl(blk_schid); /* no return */

I believe both of these issues to be the same as we are currently 
discussion in our replies to patch #10. My opinion posted there applies 
to this scenario. If my information is incorrect or you disagree with my 
assessment please yell at me! :-D


--
-- Jason J. Herne (address@hidden)