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| author | Markus Schneider-Pargmann <msp@baylibre.com> | 2025-08-19 09:52:41 +0200 |
|---|---|---|
| committer | Daniel Lezcano <daniel.lezcano@linaro.org> | 2025-09-23 12:41:58 +0200 |
| commit | 1c4b87c921fb158d853adcb8fd48c2dc07fc6f91 (patch) | |
| tree | 09807b2a1f321cb33fded96111e0007341086f2f /drivers/clocksource/Kconfig | |
| parent | 21b8a635f3b3d6a165fa257808ed381c13c72e9b (diff) | |
| download | linux-next-1c4b87c921fb158d853adcb8fd48c2dc07fc6f91.tar.gz linux-next-1c4b87c921fb158d853adcb8fd48c2dc07fc6f91.zip | |
clocksource/drivers/arm_global_timer: Add auto-detection for initial prescaler values
am43xx has a clock tree where the global timer clock is an indirect child
of the CPU clock used for frequency scaling:
dpll_mpu_ck -- CPU/cpufreq
|
v
dpll_mpu_m2_ck -- divider
|
v
mpu_periphclk -- fixed divider by 2 used for global timer
When CPU frequency changes, the global timer's clock notifier rejects
the change because the hardcoded prescaler (1 or 2) cannot accommodate
the frequency range across all CPU OPPs (300, 600, 720, 800, 1000 MHz).
Add platform-specific prescaler auto-detection to solve this issue:
- am43xx: prescaler = 50 (calculated as initial_freq/GCD of all OPP
freqs) This allows the timer to work across all CPU frequencies after
the fixed divider by 2. Tested on am4372-idk-evm.
- zynq-7000: prescaler = 2 (preserves previous Kconfig default)
- Other platforms: prescaler = 1 (previous default)
The Kconfig option now defaults to 0 (auto-detection) but can still
override the auto-detected value when set to a non-zero value,
preserving existing customization workflows.
Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Patrice Chotard <patrice.chotard@foss.st.com>
Tested-by: Judith Mendez <jm@ti.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20250819-topic-am43-arm-global-timer-v6-16-v2-1-6d082e2a5161@baylibre.com
Diffstat (limited to 'drivers/clocksource/Kconfig')
| -rw-r--r-- | drivers/clocksource/Kconfig | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index 0fd662f67d29..ffcd23668763 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -395,8 +395,7 @@ config ARM_GLOBAL_TIMER config ARM_GT_INITIAL_PRESCALER_VAL int "ARM global timer initial prescaler value" - default 2 if ARCH_ZYNQ - default 1 + default 0 depends on ARM_GLOBAL_TIMER help When the ARM global timer initializes, its current rate is declared @@ -406,6 +405,7 @@ config ARM_GT_INITIAL_PRESCALER_VAL bounds about how much the parent clock is allowed to decrease or increase wrt the initial clock value. This affects CPU_FREQ max delta from the initial frequency. + Use 0 to use auto-detection in the driver. config ARM_TIMER_SP804 bool "Support for Dual Timer SP804 module" |