Hi Andrew,
Many thanks for this. Comments below.
On 2020-01-20 13:08, Andrew Jones wrote:
Two UAPI system register IDs do not derive their values from the
ARM system register encodings. This is because their values were
accidentally swapped. As the IDs are API, they cannot be changed.
Add XXX notes to point them out.
Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
---
Documentation/virt/kvm/api.txt | 8 ++++++++
arch/arm64/include/uapi/asm/kvm.h | 11 +++++++++--
2 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/Documentation/virt/kvm/api.txt
b/Documentation/virt/kvm/api.txt
index ebb37b34dcfc..11556fc457c3 100644
--- a/Documentation/virt/kvm/api.txt
+++ b/Documentation/virt/kvm/api.txt
@@ -2196,6 +2196,14 @@ arm64 CCSIDR registers are demultiplexed by
CSSELR value:
arm64 system registers have the following id bit patterns:
0x6030 0000 0013 <op0:2> <op1:3> <crn:4> <crm:4> <op2:3>
+XXX: Two system register IDs do not follow the specified pattern.
These
+ are KVM_REG_ARM_TIMER_CVAL and KVM_REG_ARM_TIMER_CNT, which map
to
+ system registers CNTV_CVAL_EL0 and CNTVCT_EL0 respectively.
These
+ two had their values accidentally swapped, which means TIMER_CVAL
is
+ derived from the register encoding for CNTVCT_EL0 and TIMER_CNT
is
+ derived from the register encoding for CNTV_CVAL_EL0. As this is
+ API, it must remain this way.
Is 'XXX' an establiched way of documenting this kind of misfeature?
I couldn't find any other occurrence in Documentation, but I haven't
searched very hard.
If nobody has a better idea, I'll queue it as is.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
