On 2025-10-15 07:48, Ahmad Fatoum wrote:
Hello Kaustabh,
On 14.10.25 09:22, Kaustabh Chakraborty wrote:
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.
Why not read it from the clock-frequency property in the device tree?
This is what barebox is now doing, incidentally also for Samsung
support, see:
https://lore.kernel.org/barebox/[email protected]/
In barebox, the timer is a device driver, like in linux. In U-Boot
however, it is
instead part of the ARM architecture specific code. And it is being
accessed by
a single function, not dependent on others.
However, in U-Boot i found gd->arch.timer_rate_hz, which can be used,
like so:
if (gd->arch.timer_rate_hz)
return gd->arch.timer_rate_hz;
This property needs to be set in board file – in timer_init(). So I will
do
that instead.
Cheers,
Ahmad
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,
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