In devices where the U-Boot is used as a secondary bootloader, we rely on the device's primary bootloader to implement CNTFRQ_EL0. However, this reliance may lead to a non-functional timer in broken firmware.
For instance, some versions of Samsung's S-Boot don't implement it. It's also not possible to set it in the U-Boot, because it's booted in a lower exception level. CNTFRQ_EL0 is reported to be 0. Thus, the only solution is to add a config option which, when enabled, returns a hard coded value (CONFIG_COUNTER_FREQUENCY) instead of querying CNTFRQ_EL0. Signed-off-by: Kaustabh Chakraborty <[email protected]> --- arch/arm/cpu/armv8/Kconfig | 9 +++++++++ arch/arm/cpu/armv8/generic_timer.c | 4 ++++ 2 files changed, 13 insertions(+) diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig index 199335cd6040d30a355a7fd5448a449fa7f550fb..d54d874b7caea200e1c05f522d8affe6d239a102 100644 --- a/arch/arm/cpu/armv8/Kconfig +++ b/arch/arm/cpu/armv8/Kconfig @@ -4,6 +4,15 @@ config CMO_BY_VA_ONLY bool "Force cache maintenance to be exclusively by VA" depends on !SYS_DISABLE_DCACHE_OPS +config ARMV8_CNTFRQ_BROKEN + bool "Fix broken ARMv8 generic timer" + depends on COUNTER_FREQUENCY > 0 + depends on SYS_ARCH_TIMER + help + Say Y here if there is no trustable firmware present which sets + CNTFRQ_EL0 frequency before U-Boot. U-Boot will use the + CONFIG_COUNTER_FREQUENCY value as the reported frequency. + config ARMV8_SPL_EXCEPTION_VECTORS bool "Install crash dump exception vectors" depends on SPL diff --git a/arch/arm/cpu/armv8/generic_timer.c b/arch/arm/cpu/armv8/generic_timer.c index 1de7ec596fc7cbbc3e78a241f163bc0a4fcad6b6..409570cf6fda79527e296b958368b552900524b1 100644 --- a/arch/arm/cpu/armv8/generic_timer.c +++ b/arch/arm/cpu/armv8/generic_timer.c @@ -19,6 +19,10 @@ DECLARE_GLOBAL_DATA_PTR; unsigned long notrace get_tbclk(void) { unsigned long cntfrq; + + if (IS_ENABLED(CONFIG_ARMV8_CNTFRQ_BROKEN)) + return CONFIG_COUNTER_FREQUENCY; + asm volatile("mrs %0, cntfrq_el0" : "=r" (cntfrq)); return cntfrq; } --- base-commit: a5b3be1a37e19646b9d36c91f11b23f568be4f21 change-id: 20251014-armv8-broken-cntfrq-f350f68fbf6e Best regards, -- Kaustabh Chakraborty <[email protected]>
