ARM: EXYNOS: Allow to use architected timer

Quoted 7 lines · Pavel Fedin

Hello!

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IIRC the use of the CP15 timer is not reliable on this platform. I don't have a link ready, but this has come up a few times.

I know that Samsung SoC guys are not very keen on this, therefore i actually made this optional.

No, it's not a good way and it's not an optional problem...I think, I already commented many times about that...If we can arch timer on exynos stuff, why we are still using MCT...? hmm...

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If
you want, you could omit the second patch, and by default Exynos platform will use MCT. But if someone wants to use KVM, it would be enough only to modify device tree in order to enable CP15. Would this be a good compromise?

No, because the MCT should be used by default _always_ and it is depending on hardware scheme...

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Regarding KVM usage, would it be possible to emulate the architected timer from qemu instead?

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Unfortunately no. Accesses to virtual timer registers cannot be trapped. It is possible to trap
physical timer accesses, and trick the kernel into using it, but it's slow, and it is a different story, which you can read here: http://www.spinics.net/lists/kvm/msg121714.html.
So, i think that having an option to use CP15 would be a good solution. It is known to work, and i
use this configuration here on SMDK5410 without any problems.

Actually Exynos5410 has been designed differently so it is safe only on smdk5410 not others...

- Kukjin