Re: [PATCH v2 1/1] ArmPkg/TimerDxe: Add ISB for timer compare value reload

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 15 March 2018 at 09:40, Marc Zyngier <marc.zyngier@arm.com> wrote:
> On 15/03/18 07:30, Ard Biesheuvel wrote:
>> On 15 March 2018 at 07:11, Guo Heyi <heyi.guo@linaro.org> wrote:
>>> Hi Marc and Ard,
>>>
>>> I found the timer re-enable code was added by Ard for special reason:
>>>
>>> commit b1a633434ddc5fc28de817debd963f7845fb78c7
>>> Author: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>> Date:   Thu Sep 18 21:16:47 2014 +0000
>>>
>>>     ArmPkg/TimerDxe: add workaround for KVM timer interrupt handling
>>>
>>> So this line of code cannot be removed and I will add an ISB after enabling
>>> timer.
>>>
>>
>> I'm not sure. IIUC, the KVM issue that required this has been fixed
>> long ago, and I don't want to carry this forever. Marc?
>
> This has been fixed quite a while ago:
>
> commit f120cd6533d21075ab103ae6c225b1697853660d
> Author: Marc Zyngier <marc.zyngier@arm.com>
> Date:   Mon Jun 23 13:59:13 2014 +0100
>
>     KVM: arm/arm64: timer: Allow the timer to control the active state
>
>     In order to remove the crude hack where we sneak the masked bit
>     into the timer's control register, make use of the phys_irq_map
>     API control the active state of the interrupt.
>
>     This causes some limited changes to allow for potential error
>     propagation.
>
>     Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>     Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>

Does this mean we can lose this as well?

https://github.com/tianocore/edk2/blob/master/ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c#L31


>>> Another strange thing is that we got lots of "Spurious GIC interrupt" error
>>> messages when timer enable code was removed, though at last it could boot to EFI
>>> shell. Please let me know if you have any idea about the possible reason of this
>>> issue.
>>>
>>
>> No idea, sorry.
>
> Me neither. You'd have to dump the control register before and after,
> and work out what is being changed exactly.
>
> Thanks,
>
>         M.
> --
> Jazz is not dead. It just smells funny...