On 2020-01-20 13:51, Andrew Jones wrote:
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.
My personal preference would be for a big fat "*WARNING*" (with
an optional <blink> attribute), and a link to a picture of me
wearing a brown paper bag on my head.
But maybe "WARNING" is enough. Dunno. Anyway, if nobody comes up
with a better idea by tomorrow, I'll take it as is.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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