From mboxrd@z Thu Jan 1 00:00:00 1970 From: kgene@kernel.org (Kukjin Kim) Date: Tue, 06 Oct 2015 19:09:58 +0900 Subject: [PATCH 0/2] ARM: EXYNOS: Allow to use architected timer In-Reply-To: <00d801d10014$e6d994a0$b48cbde0$@samsung.com> References: <6613638.q5qyQZxXy7@wuerfel> <00d801d10014$e6d994a0$b48cbde0$@samsung.com> Message-ID: <187701d1001f$284b1350$78e139f0$@kernel.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Pavel Fedin wrote: > > Hello! > > > 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... > 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... > > Regarding KVM usage, would it be possible to emulate the architected > > timer from qemu instead? > > 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