Re: [PATCH v3 4/8] drivers: arm_architected_timer: refactor for pbl compatibility

On 2026-08-17 16:01, Stefan Kerkmann wrote:
> All ARMv8-A cores implement the 64bit wide generic timer CNTPCT[1]. Thus
> the driver is the candidate for all AARCH64 SoCs to implement
> PBL_CLOCKSOURCE compatibilty.
> 
> There is one catch though: the CNTFRQ_EL0 register[2] must be programmed
> by the bootrom, barebox or the tf-a before the `arm_arch_timer_init`
> call or the clocksource setup will return with -ENODEV. A later
> re-initialization is also possible by calling `arm_arch_timer_init`
> again.
> 
> [1]: See "ARM Architecture Reference Manual for A-profile architecture
> (rev L.a)", chapter D12 "The Generic Timer in AArch64 state"
> [2]: See "ARM Architecture Reference Manual for A-profile architecture
> (rev L.a)", chapter D12.1.2.1 "Initializing and reading the system
> effective frequency"
> 
> Signed-off-by: Stefan Kerkmann <[email protected]>
> ---
>  .../include/asm/hardware/arm_architected_timer.h   | 21 +++++++++++++++++++
>  drivers/clocksource/Makefile                       |  2 +-
>  drivers/clocksource/arm_architected_timer.c        | 24 ++++++++++++++--------
>  3 files changed, 38 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/include/asm/hardware/arm_architected_timer.h b/arch/arm/include/asm/hardware/arm_architected_timer.h
> new file mode 100644
> index 0000000000..e0c1fd84fd
> --- /dev/null
> +++ b/arch/arm/include/asm/hardware/arm_architected_timer.h
> @@ -0,0 +1,21 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef __ASM_ARM_HARDWARE_ARCH_TIMER_H
> +#define __ASM_ARM_HARDWARE_ARCH_TIMER_H
> +
> +#include <linux/types.h>
> +
> +/**
> + * arm_arch_timer_init() - Initialize the ARM architected timer as global
> + * clocksource
> + * @cntfrq: The timer frequency, if zero the frequency is read from the
> + *          CNTFRQ_EL0 register
> + *
> + * This function is meant to be called in a PBL constructor or in the driver
> + * probe function.
> + *
> + * Return: 0 on success, -ENODEV if the timer frequency can not be determined
> + */
> +int arm_arch_timer_init(uint64_t cntfrq);
> +
> +#endif
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index dff8255650..0c92477247 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -13,7 +13,7 @@ obj-$(CONFIG_CLOCKSOURCE_ORION)   += orion.o
>  obj-$(CONFIG_CLOCKSOURCE_UEMD)    += uemd.o
>  obj-$(CONFIG_CLOCKSOURCE_ROCKCHIP)+= rk_timer.o
>  obj-$(CONFIG_CLOCKSOURCE_ATMEL_PIT) += timer-atmel-pit.o
> -obj-$(CONFIG_CLOCKSOURCE_ARM_ARCHITECTED_TIMER) += arm_architected_timer.o
> +obj-pbl-$(CONFIG_CLOCKSOURCE_ARM_ARCHITECTED_TIMER) += arm_architected_timer.o
>  ifneq ($(CONFIG_CPU_V8),y)
>  CFLAGS_arm_architected_timer.o := -march=armv7-a
>  endif
> diff --git a/drivers/clocksource/arm_architected_timer.c b/drivers/clocksource/arm_architected_timer.c
> index daced94c0e..ea5f5b8e05 100644
> --- a/drivers/clocksource/arm_architected_timer.c
> +++ b/drivers/clocksource/arm_architected_timer.c
> @@ -9,6 +9,7 @@
>  #include <linux/clk.h>
>  #include <io.h>
>  #include <asm/system.h>
> +#include <asm/hardware/arm_architected_timer.h>
>  
>  static uint64_t arm_arch_clocksource_read(void)
>  {
> @@ -22,22 +23,29 @@ static struct clocksource cs = {
>  	.priority = 70,
>  };
>  
> -static int arm_arch_timer_probe(struct device *dev)
> +int arm_arch_timer_init(uint64_t cntfrq)
>  {
> -	u32 cntfrq;
> -	int ret;
> -
> -	/* Some platforms don't set CNTFRQ_EL0 before barebox */
> -	ret = of_property_read_u32(dev->of_node, "clock-frequency", &cntfrq);
> -
> -	if (ret)
> +	if (!cntfrq)
>  		cntfrq = get_cntfrq();

I wonder if we should just drop the cntfrq argument. All users call
set_cntfrq() before calling this, so get_cntfrq() should return the
correct value and we can rely on it.

Sascha

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