Messages in this thread | | | Subject | Re: [PATCH 1/2] clocksource/drivers/exynos_mct: Prioritise Arm arch timer on arm64 | From | Krzysztof Kozlowski <> | Date | Wed, 9 Jun 2021 13:41:33 +0200 |
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On 08/06/2021 17:43, Will Deacon wrote: > All arm64 CPUs feature an architected timer, which offers a relatively > low-latency interface to a per-cpu clocksource and timer. For the most > part, using this interface is a no-brainer, with the exception of SoCs > where it cannot be used to wake up from deep idle state (i.e. > CLOCK_EVT_FEAT_C3STOP is set). > > On the contrary, the Exynos MCT is extremely slow to access yet can be > used as a wakeup source. In preparation for using the Exynos MCT as a > potential wakeup timer for the Arm architected timer, reduce its ratings > so that the architected timer is preferred. > > This effectively reverts the decision made in 6282edb72bed > ("clocksource/drivers/exynos_mct: Increase priority over ARM arch timer") > for arm64, as the reasoning for the original change was to work around > a 32-bit SoC design. > > Cc: Marek Szyprowski <m.szyprowski@samsung.com> > Cc: Krzysztof Kozlowski <krzk@kernel.org> > Cc: Chanwoo Choi <cw00.choi@samsung.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Will Deacon <will@kernel.org> > --- > drivers/clocksource/exynos_mct.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c > index fabad79baafc..804d3e01c8f4 100644 > --- a/drivers/clocksource/exynos_mct.c > +++ b/drivers/clocksource/exynos_mct.c > @@ -51,6 +51,15 @@ > > #define TICK_BASE_CNT 1 > > +#ifdef CONFIG_ARM > +/* Use values higher than ARM arch timer. See 6282edb72bed. */ > +#define MCT_CLKSOURCE_RATING 450 > +#define MCT_CLKEVENTS_RATING 500 > +#else > +#define MCT_CLKSOURCE_RATING 350 > +#define MCT_CLKEVENTS_RATING 350 > +#endif > +
Tested on Exynos5422 (32-bit ARM) and it seems to work. I don't have ARMv8 board to check it. We want Exynos MCT on ARMv8 as well, because unfortunately it shares the block with Arch timer. This was investigated by Marek: https://lore.kernel.org/linux-samsung-soc/20181017123622eucas1p14654c89a8590fd094d638b60ab9af8f0~eZY3j27rs0422004220eucas1p1M@eucas1p1.samsung.com/
Best regards, Krzysztof
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