linux-kernel - Re: [PATCH 2/4] RISC-V: Support per-hart timebase-frequency

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Date:   Fri, 07 Dec 2018 08:42:30 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     atish.patra@....com
CC:     linux-kernel@...r.kernel.org, atish.patra@....com,
        aou@...s.berkeley.edu, daniel.lezcano@...aro.org,
        devicetree@...r.kernel.org, dmitriy@...-tech.org,
        linux-riscv@...ts.infradead.org, mark.rutland@....com,
        robh+dt@...nel.org, tglx@...utronix.de, anup@...infault.org,
        Damien.LeMoal@....com
Subject:     Re: [PATCH 2/4] RISC-V: Support per-hart timebase-frequency

On Mon, 03 Dec 2018 12:57:29 PST (-0800), atish.patra@....com wrote:
> Follow the updated DT specs and read the timebase-frequency
> from the boot cpu. Keep the old DT reading as well for backward
> compatibility. This patch is rework of old patch from Palmer.
>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
>  arch/riscv/kernel/time.c          |  9 +--------
>  drivers/clocksource/riscv_timer.c | 22 ++++++++++++++++++++++
>  2 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/kernel/time.c b/arch/riscv/kernel/time.c
> index 1911c8f6..225fe743 100644
> --- a/arch/riscv/kernel/time.c
> +++ b/arch/riscv/kernel/time.c
> @@ -20,14 +20,7 @@ unsigned long riscv_timebase;
>
>  void __init time_init(void)
>  {
> -	struct device_node *cpu;
> -	u32 prop;
> -
> -	cpu = of_find_node_by_path("/cpus");
> -	if (!cpu || of_property_read_u32(cpu, "timebase-frequency", &prop))
> -		panic(KERN_WARNING "RISC-V system with no 'timebase-frequency' in DTS\n");
> -	riscv_timebase = prop;
> +	timer_probe();
>
>  	lpj_fine = riscv_timebase / HZ;
> -	timer_probe();
>  }
> diff --git a/drivers/clocksource/riscv_timer.c b/drivers/clocksource/riscv_timer.c
> index 084e97dc..96af7058 100644
> --- a/drivers/clocksource/riscv_timer.c
> +++ b/drivers/clocksource/riscv_timer.c
> @@ -83,6 +83,26 @@ void riscv_timer_interrupt(void)
>  	evdev->event_handler(evdev);
>  }
>
> +static long __init riscv_timebase_frequency(struct device_node *node)
> +{
> +	u32 timebase;
> +
> +	if (!of_property_read_u32(node, "timebase-frequency", &timebase))
> +		return timebase;
> +
> +	/*
> +	 * As per the DT specification, timebase-frequency should be present
> +	 * under individual cpu node. Unfortunately, there are already available
> +	 * HiFive Unleashed devices where the timebase-frequency entry is under
> +	 * CPUs. check under parent "cpus" node to cover those devices.
> +	 */
> +	if (!of_property_read_u32(node->parent, "timebase-frequency",
> +				  &timebase))
> +		return timebase;
> +
> +	panic("RISC-V system with no 'timebase-frequency' in DTS\n");
> +}
> +
>  static int __init riscv_timer_init_dt(struct device_node *n)
>  {
>  	int cpuid, hartid, error;
> @@ -94,6 +114,8 @@ static int __init riscv_timer_init_dt(struct device_node *n)
>  	if (cpuid != smp_processor_id())
>  		return 0;
>
> +	/* This should be called only for boot cpu */
> +	riscv_timebase = riscv_timebase_frequency(n);
>  	cs = per_cpu_ptr(&riscv_clocksource, cpuid);
>  	clocksource_register_hz(cs, riscv_timebase);

We need to check to make sure the timebase-frequency of each hart is the same.  
This is mandated by the RISC-V ISA specification but should be checked in the 
code.