-ENXIO The group or attribute is unknown/unsupported for this device
or hardware support is missing.
-EFAULT Invalid user pointer for attr->addr.
+ -EBUSY Attempt to write a register that is read-only after
+ initialization
======= =============================================================
Note that distributor fields are not banked, but return the same value
regardless of the mpidr used to access the register.
+ Userspace is allowed to write the following register fields prior to
+ initialization of the VGIC:
+
+ =====================
+ GICD_IIDR.Revision
+ GICD_TYPER2.nASSGIcap
+ =====================
+
+
GICD_IIDR.Revision is updated when the KVM implementation is changed in a
way directly observable by the guest or userspace. Userspace should read
GICD_IIDR from KVM and write back the read value to confirm its expected
behavior.
+ GICD_TYPER2.nASSGIcap allows userspace to control the support of SGIs
+ without an active state. At VGIC creation the field resets to the
+ maximum capability of the system. Userspace is expected to read the field
+ to determine the supported value(s) before writing to the field.
+
+
The GICD_STATUSR and GICR_STATUSR registers are architecturally defined such
that a write of a clear bit has no effect, whereas a write with a set bit
clears that value. To allow userspace to freely set the values of these two