Re: [kvm-unit-tests PATCH v2 6/9] s390x: css: stsch, enumeration test

Cornelia Huck
2019-12-02T19:49:36Z

On Mon, 2 Dec 2019 19:33:59 +0100
Pierre Morel <pmorel@linux.ibm.com> wrote:

> On 2019-12-02 19:15, Cornelia Huck wrote:
> > On Mon, 2 Dec 2019 18:53:16 +0100
> > Pierre Morel <pmorel@linux.ibm.com> wrote:
> >
> >> On 2019-12-02 15:22, Cornelia Huck wrote:
> >>> On Thu, 28 Nov 2019 13:46:04 +0100
> >>> Pierre Morel <pmorel@linux.ibm.com> wrote:
> >
> >>>> +static int test_device_sid;
> >>>> +
> >>>> +static void test_enumerate(void)
> >>>> +{
> >>>> + struct pmcw *pmcw = &schib.pmcw;
> >>>> + int sid;
> >>>> + int ret, i;
> >>>> + int found = 0;
> >>>> +
> >>>> + for (sid = 0; sid < 0xffff; sid++) {
> >>>> + ret = stsch(sid|SID_ONE, &schib);
> >>>
> >>> This seems a bit odd. You are basically putting the subchannel number
> >>> into sid, OR in the one, and then use the resulting value as the sid
> >>> (subchannel identifier).
> >>>
> >>>> + if (!ret && (pmcw->flags & PMCW_DNV)) {
> >>>> + report_info("SID %04x Type %s PIM %x", sid,
> >>>
> >>> That's not a sid, but the subchannel number (see above).
> >>>
> >>>> + Channel_type[pmcw->st], pmcw->pim);
> >>>> + for (i = 0; i < 8; i++) {
> >>>> + if ((pmcw->pim << i) & 0x80) {
> >>>> + report_info("CHPID[%d]: %02x", i,
> >>>> + pmcw->chpid[i]);
> >>>> + break;
> >>>> + }
> >>>> + }
> >>>> + found++;
> >>>> +
> >>>> + }
> >>>
> >>> Here, you iterate over the 0-0xffff range, even if you got a condition
> >>> code 3 (indicating no more subchannels in that set). Is that
> >>> intentional?
> >>
> >> I thought there could be more subchannels.
> >> I need then a break in the loop when this happens.
> >> I will reread the PoP to see how to find that no more subchannel are in
> >> that set.
> >
> > The fact that cc 3 for stsch == no more subchannels is unfortunately a
> > bit scattered across the PoP :/ Dug it out some time ago, maybe it's
> > still in the archives somewhere...
>
> So the the subchannel are always one after the other?

While QEMU (and z/VM) usually do that, they can really be scattered
around. For the in-between I/O subchannels that don't lead to a device,
you'll still get cc 0, it's just the dnv bit that is 0. The cc 3
basically just tells you that you can stop looking.