Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20200605' into staging

s390x update:
- enhance s390x documentation
- allow ORBs without prefetch specified for vfio-ccw
- various cleanups and enhancements

# gpg: Signature made Fri 05 Jun 2020 16:32:43 BST
# gpg:                using RSA key C3D0D66DC3624FF6A8C018CEDECF6B93C6F02FAF
# gpg:                issuer "cohuck@redhat.com"
# gpg: Good signature from "Cornelia Huck <conny@cornelia-huck.de>" [marginal]
# gpg:                 aka "Cornelia Huck <huckc@linux.vnet.ibm.com>" [full]
# gpg:                 aka "Cornelia Huck <cornelia.huck@de.ibm.com>" [full]
# gpg:                 aka "Cornelia Huck <cohuck@kernel.org>" [marginal]
# gpg:                 aka "Cornelia Huck <cohuck@redhat.com>" [marginal]
# Primary key fingerprint: C3D0 D66D C362 4FF6 A8C0  18CE DECF 6B93 C6F0 2FAF

* remotes/cohuck/tags/s390x-20200605:
  target/s390x: Restrict system-mode declarations
  target/s390x/helper: Clean ifdef'ry
  target/s390x: Only compile decode_basedisp() on system-mode
  MAINTAINERS: add Thomas as additional s390x maintainer
  docs/s390x: document vfio-ccw
  vfio-ccw: allow non-prefetch ORBs
  docs/s390x: document 3270
  docs/s390x: document the virtual css
  s390x: pv: Fix KVM_PV_PREP_RESET command wrapper name
  s390x/kvm: help valgrind in several places

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 86 insertions, 0 deletions

diff --git a/docs/system/s390x/css.rst b/docs/system/s390x/css.rst
new file mode 100644
index 0000000000..3b40161184
--- /dev/null
+++ b/docs/system/s390x/css.rst
@@ -0,0 +1,86 @@
+The virtual channel subsystem
+=============================
+
+QEMU implements a virtual channel subsystem with subchannels, (mostly
+functionless) channel paths, and channel devices (virtio-ccw, 3270, and
+devices passed via vfio-ccw). It supports multiple subchannel sets (MSS) and
+multiple channel subsystems extended (MCSS-E).
+
+All channel devices support the ``devno`` property, which takes a parameter
+in the form ``<cssid>.<ssid>.<device number>``.
+
+The default channel subsystem image id (``<cssid>``) is ``0xfe``. Devices in
+there will show up in channel subsystem image ``0`` to guests that do not
+enable MCSS-E. Note that devices with a different cssid will not be visible
+if the guest OS does not enable MCSS-E (which is true for all supported guest
+operating systems today).
+
+Supported values for the subchannel set id (``<ssid>``) range from ``0-3``.
+Devices with a ssid that is not ``0`` will not be visible if the guest OS
+does not enable MSS (any Linux version that supports virtio also enables MSS).
+Any device may be put into any subchannel set, there is no restriction by
+device type.
+
+The device number can range from ``0-0xffff``.
+
+If the ``devno`` property is not specified for a device, QEMU will choose the
+next free device number in subchannel set 0, skipping to the next subchannel
+set if no more device numbers are free.
+
+QEMU places a device at the first free subchannel in the specified subchannel
+set. If a device is hotunplugged and later replugged, it may appear at a
+different subchannel. (This is similar to how z/VM works.)
+
+
+Examples
+--------
+
+* a virtio-net device, cssid/ssid/devno automatically assigned::
+
+    -device virtio-net-ccw
+
+  In a Linux guest (without default devices and no other devices specified
+  prior to this one), this will show up as ``0.0.0000`` under subchannel
+  ``0.0.0000``.
+
+  The auto-assigned-properties in QEMU (as seen via e.g. ``info qtree``)
+  would be ``dev_id = "fe.0.0000"`` and ``subch_id = "fe.0.0000"``.
+
+* a virtio-rng device in subchannel set ``0``::
+
+    -device virtio-rng-ccw,devno=fe.0.0042
+
+  If added to the same Linux guest as above, it would show up as ``0.0.0042``
+  under subchannel ``0.0.0001``.
+
+  The properties for the device would be ``dev_id = "fe.0.0042"`` and
+  ``subch_id = "fe.0.0001"``.
+
+* a virtio-gpu device in subchannel set ``2``::
+
+    -device virtio-gpu-ccw,devno=fe.2.1111
+
+  If added to the same Linux guest as above, it would show up as ``0.2.1111``
+  under subchannel ``0.2.0000``.
+
+  The properties for the device would be ``dev_id = "fe.2.1111"`` and
+  ``subch_id = "fe.2.0000"``.
+
+* a virtio-mouse device in a non-standard channel subsystem image::
+
+    -device virtio-mouse-ccw,devno=2.0.2222
+
+  This would not show up in a standard Linux guest.
+
+  The properties for the device would be ``dev_id = "2.0.2222"`` and
+  ``subch_id = "2.0.0000"``.
+
+* a virtio-keyboard device in another non-standard channel subsystem image::
+
+    -device virtio-keyboard-ccw,devno=0.0.1234
+
+  This would not show up in a standard Linux guest, either, as ``0`` is not
+  the standard channel subsystem image id.
+
+  The properties for the device would be ``dev_id = "0.0.1234"`` and
+  ``subch_id = "0.0.0000"``.