On Thu, 31 Jan 2019 12:31:00 -0500
Farhan Ali <al...@linux.ibm.com> wrote:
> On 01/29/2019 08:29 AM, Jason J. Herne wrote:
> > Add struct for format-0 ccws. Support executing format-0 channel
> > programs and waiting for their completion before continuing execution.
> > This will be used for real dasd ipl.
> >
> > Add cu_type() to channel io library. This will be used to query control
> > unit type which is used to determine if we are booting a virtio device or a
> > real dasd device.
> >
> > Signed-off-by: Jason J. Herne<jjhe...@linux.ibm.com>
> > ---
> > pc-bios/s390-ccw/cio.c | 114 +++++++++++++++++++++++++++++++++++++++
> > pc-bios/s390-ccw/cio.h | 127
> > ++++++++++++++++++++++++++++++++++++++++++--
> > pc-bios/s390-ccw/s390-ccw.h | 1 +
> > pc-bios/s390-ccw/start.S | 33 +++++++++++-
> > 4 files changed, 270 insertions(+), 5 deletions(-)
> > +/*
> > + * Executes a channel program at a given subchannel. The request to run the
> > + * channel program is sent to the subchannel, we then wait for the
> > interrupt
> > + * signaling completion of the I/O operation(s) performed by the channel
> > + * program. Lastly we verify that the i/o operation completed without
> > error and
> > + * that the interrupt we received was for the subchannel used to run the
> > + * channel program.
> > + *
> > + * Note: This function assumes it is running in an environment where no
> > other
> > + * cpus are generating or receiving I/O interrupts. So either run it in a
> > + * single-cpu environment or make sure all other cpus are not doing I/O and
> > + * have I/O interrupts masked off.
> > + */
> > +int do_cio(SubChannelId schid, uint32_t ccw_addr, int fmt)
> > +{
> > + CmdOrb orb = {};
> > + Irb irb = {};
> > + sense_data_eckd_dasd sd;
> > + int rc, retries = 0;
> > +
> > + IPL_assert(fmt == 0 || fmt == 1, "Invalid ccw format");
> > +
> > + /* ccw_addr must be <= 24 bits and point to at least one whole ccw. */
> > + if (fmt == 0) {
> > + IPL_assert(ccw_addr <= 0xFFFFFF - 8, "Invalid ccw address");
> > + }
> > +
> > + orb.fmt = fmt ;
> > + orb.pfch = 1; /* QEMU's cio implementation requires prefetch */
> > + orb.c64 = 1; /* QEMU's cio implementation requires 64-bit idaws */
> > + orb.lpm = 0xFF; /* All paths allowed */
> > + orb.cpa = ccw_addr;
> > +
> > + while (true) {
> > + rc = ssch(schid, &orb);
> > + if (rc == 1) {
> > + /* Status pending, not sure why. Let's eat the status and
> > retry. */
> > + tsch(schid, &irb);
> > + retries++;
> > + continue;
> > + }
> > + if (rc) {
> > + print_int("ssch failed with rc=", rc);
> > + break;
> > + }
> > +
> > + consume_io_int();
> > +
> > + /* collect status */
> > + rc = tsch(schid, &irb);
> > + if (rc) {
> > + print_int("tsch failed with rc=", rc);
> > + break;
> > + }
> > +
> > + if (!irb_error(&irb)) {
> > + break;
> > + }
> > +
> > + /*
> > + * Unexpected unit check, or interface-control-check. Use sense to
> > + * clear unit check then retry.
> > + */
> > + if ((unit_check(&irb) || iface_ctrl_check(&irb)) && retries <= 2) {
> > + basic_sense(schid, &sd, sizeof(sd));
>
> We are using basic sense to clear any unit check or ifcc, but is it
> possible for the basic sense to cause another unit check?
>
> The chapter on Basic Sense in the Common I/O Device Commands
> (http://publibz.boulder.ibm.com/support/libraryserver/FRAMESET/dz9ar501/2.1?SHELF=&DT=19920409154647&CASE=)
>
> says this:
>
> ""
> The basic sense command initiates a sense operation at all devices
> and cannot cause the command-reject, intervention-required,
> data-check, or overrun bit to be set to one. If the control unit
> detects an equipment malfunction or invalid checking-block code
> (CBC) on the sense-command code, the equipment-check or bus-out-check
> bit is set to one, and unit check is indicated in the device-status
> byte.
> ""
>
> If my understanding is correct, if there is an equipment malfunction
> then the control unit can return a unit check even for a basic sense.
> This can lead to infinite recursion in the bios.
I think the retries variable is supposed to take care of that.
What I don't understand is why we do the basic sense after an IFCC?
Wouldn't it make more sense to simply retry the original command in
that case?
>
>
>
> > + retries++;
> > + continue;
> > + }
> > +
> > + break;
> > + }
> > +
> > + return rc;
> > +}
>
