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clocksource/drivers/exynos_mct: Prioritise Arm arch timer on arm64

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>
Tested-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com> # exynos-5422
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210608154341.10794-2-will@kernel.org

authored by

Will Deacon and committed by
Daniel Lezcano ae460fd9 f80e2148

+11 -2
+11 -2
drivers/clocksource/exynos_mct.c
··· 51 51 52 52 #define TICK_BASE_CNT 1 53 53 54 + #ifdef CONFIG_ARM 55 + /* Use values higher than ARM arch timer. See 6282edb72bed. */ 56 + #define MCT_CLKSOURCE_RATING 450 57 + #define MCT_CLKEVENTS_RATING 500 58 + #else 59 + #define MCT_CLKSOURCE_RATING 350 60 + #define MCT_CLKEVENTS_RATING 350 61 + #endif 62 + 54 63 enum { 55 64 MCT_INT_SPI, 56 65 MCT_INT_PPI ··· 215 206 216 207 static struct clocksource mct_frc = { 217 208 .name = "mct-frc", 218 - .rating = 450, /* use value higher than ARM arch timer */ 209 + .rating = MCT_CLKSOURCE_RATING, 219 210 .read = exynos4_frc_read, 220 211 .mask = CLOCKSOURCE_MASK(32), 221 212 .flags = CLOCK_SOURCE_IS_CONTINUOUS, ··· 466 457 evt->set_state_oneshot_stopped = set_state_shutdown; 467 458 evt->tick_resume = set_state_shutdown; 468 459 evt->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT; 469 - evt->rating = 500; /* use value higher than ARM arch timer */ 460 + evt->rating = MCT_CLKEVENTS_RATING, 470 461 471 462 exynos4_mct_write(TICK_BASE_CNT, mevt->base + MCT_L_TCNTB_OFFSET); 472 463