We are exporting the format of the priority field as it's stored in the
GICH_VMCR.VMPriMask field using the lower five bits when accessing
register state using the GICC_PMR offset. This is unfortunate, but it's
ABI already, so we simply have to make it clear.
Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx>
---
Documentation/virtual/kvm/devices/arm-vgic.txt | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/Documentation/virtual/kvm/devices/arm-vgic.txt b/Documentation/virtual/kvm/devices/arm-vgic.txt
index 76e61c8..975a904 100644
--- a/Documentation/virtual/kvm/devices/arm-vgic.txt
+++ b/Documentation/virtual/kvm/devices/arm-vgic.txt
@@ -83,6 +83,12 @@ Groups:
Bits for undefined preemption levels are RAZ/WI.
+ For historical reasons we export the GICC_PMR register in the format of the
+ GICH_VMCR.VMPriMask field in the lower 5 bits of a word, meaning that
+ userspace must always use the lower 5 bits to communicate with the KVM
+ device and must shift the value left by 3 places to obtain the actual
+ priority mask level.
+
Limitations:
- Priorities are not implemented, and registers are RAZ/WI
- Currently only implemented for KVM_DEV_TYPE_ARM_VGIC_V2.
--
2.9.0
