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clocksource/drivers/arm_arch_timer: Use event stream scaling when available

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With FEAT_ECV and the 1GHz counter, it is pretty likely that the
event stream divider doesn't fit in the field that holds the
divider value (we only have 4 bits to describe counter bits [15:0]

Thankfully, FEAT_ECV also provides a scaling mechanism to switch
the field to cover counter bits [23:8] instead.

Enable this on arm64 when ECV is available (32bit doesn't have
any detection infrastructure and is unlikely to be run on an
ARMv8.6 system anyway).

Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20220203170502.2694422-1-maz@kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
This commit is contained in:
Marc Zyngier 2022-02-03 17:05:02 +00:00 committed by Daniel Lezcano
parent 0a3a4b9d2b
commit 8c4b810a87
2 changed files with 12 additions and 2 deletions
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13
drivers/clocksource/arm_arch_timer.c
View file

@ -880,10 +880,19 @@ static void __arch_timer_setup(unsigned type,
clockevents_config_and_register(clk, arch_timer_rate, 0xf, max_delta);
}
static void arch_timer_evtstrm_enable(int divider)
static void arch_timer_evtstrm_enable(unsigned int divider)
{
u32 cntkctl = arch_timer_get_cntkctl();
#ifdef CONFIG_ARM64
/* ECV is likely to require a large divider. Use the EVNTIS flag. */
if (cpus_have_const_cap(ARM64_HAS_ECV) && divider > 15) {
cntkctl |= ARCH_TIMER_EVT_INTERVAL_SCALE;
divider -= 8;
}
#endif
divider = min(divider, 15U);
cntkctl &= ~ARCH_TIMER_EVT_TRIGGER_MASK;
/* Set the divider and enable virtual event stream */
cntkctl |= (divider << ARCH_TIMER_EVT_TRIGGER_SHIFT)
@ -912,7 +921,7 @@ static void arch_timer_configure_evtstream(void)
lsb++;
/* enable event stream */
arch_timer_evtstrm_enable(max(0, min(lsb, 15)));
arch_timer_evtstrm_enable(max(0, lsb));
}
static void arch_counter_set_user_access(void)

1
include/clocksource/arm_arch_timer.h
View file

@ -56,6 +56,7 @@ enum arch_timer_spi_nr {
#define ARCH_TIMER_EVT_TRIGGER_MASK (0xF << ARCH_TIMER_EVT_TRIGGER_SHIFT)
#define ARCH_TIMER_USR_VT_ACCESS_EN (1 << 8) /* virtual timer registers */
#define ARCH_TIMER_USR_PT_ACCESS_EN (1 << 9) /* physical timer registers */
#define ARCH_TIMER_EVT_INTERVAL_SCALE (1 << 17) /* EVNTIS in the ARMv8 ARM */
#define ARCH_TIMER_EVT_STREAM_PERIOD_US 100
#define ARCH_TIMER_EVT_STREAM_FREQ \