linux-kernel - Re: [PATCH v2 2/4] RISC-V: Support per-hart timebase-frequency

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Date:   Fri, 14 Dec 2018 10:24:21 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Atish Patra <atish.patra@....com>, linux-kernel@...r.kernel.org
Cc:     Albert Ou <aou@...s.berkeley.edu>, devicetree@...r.kernel.org,
        Dmitriy Cherkasov <dmitriy@...-tech.org>,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Anup Patel <anup@...infault.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v2 2/4] RISC-V: Support per-hart timebase-frequency

On 14/12/2018 00:14, Atish Patra 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 | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 32 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..75262409 100644
> --- a/drivers/clocksource/riscv_timer.c
> +++ b/drivers/clocksource/riscv_timer.c
> @@ -83,6 +83,35 @@ void riscv_timer_interrupt(void)
>  	evdev->event_handler(evdev);
>  }
>  
> +static void __init riscv_timebase_frequency(struct device_node *node,
> +					    int hartid)
> +{
> +	u32 timebase;
> +
> +	if (!of_property_read_u32(node, "timebase-frequency", &timebase))
> +		goto check;
> +
> +	/*
> +	 * 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))
> +		goto check;
> +
> +	panic("RISC-V system with no timebase-frequency in DTS for hart [%d]\n",
> +	      hartid);

no panic in the driver code please. Alternatively use pr_err and let the
timer-probe function spit the critical error on the console.

It would be nicer to add a fixed-clock and get the rate from it.

> +check:
> +	/* RISC-V ISA specification mandates that every cpu has a timer */
> +	if (!riscv_timebase)
> +		riscv_timebase = timebase;
> +	else if (riscv_timebase && riscv_timebase != timebase)
> +		pr_warn("RISC-V system with different timebase-frequency\n");
> +}
> +
>  static int __init riscv_timer_init_dt(struct device_node *n)
>  {
>  	int cpuid, hartid, error;
> @@ -90,10 +119,12 @@ static int __init riscv_timer_init_dt(struct device_node *n)
>  
>  	hartid = riscv_of_processor_hartid(n);
>  	cpuid = riscv_hartid_to_cpuid(hartid);
> +	riscv_timebase_frequency(n, hartid);
>  
>  	if (cpuid != smp_processor_id())
>  		return 0;

Somehow related to this change. Are you sure the test above makes sense?

> +	/* This should be called only for boot cpu */
>  	cs = per_cpu_ptr(&riscv_clocksource, cpuid);
>  	clocksource_register_hz(cs, riscv_timebase);
>  
> 


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