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Re: [qemu-s390x] [RFC 15/15] s390-bios: Use sense ccw to ensure consiste

From: Jason J. Herne
Subject: Re: [qemu-s390x] [RFC 15/15] s390-bios: Use sense ccw to ensure consistent device state at boot time
Date: Fri, 6 Jul 2018 10:45:03 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

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)

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