On Mon, Jan 20, 2020 at 01:26:32PM +0000, Marc Zyngier wrote: > 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. I didn't find anything claiming it was the standard way of doing it. I also considered using 'NOTE', but I was afraid it wouldn't stand out as a "problem" enough. And, even though 'BUG' would certainly stand out, I felt it implied we should be posting a fix. Anyway, I'd be happy to change it to whatever the consensus is. Thanks, drew > > If nobody has a better idea, I'll queue it as is. > > Thanks, > > M. > -- > Jazz is not dead. It just smells funny... >
