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SubjectRe: [PATCH 2/4] RISC-V: Support per-hart timebase-frequency
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On Mon, 03 Dec 2018 12:57:29 PST (-0800), atish.patra@wdc.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@wdc.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.

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