On 17/07/2020 09:50, Anup Patel wrote:
> We add a separate CLINT timer driver for Linux RISC-V M-mode (i.e.
> RISC-V NoMMU kernel).
>
> The CLINT MMIO device provides three things:
> 1. 64bit free running counter register
> 2. 64bit per-CPU time compare registers
> 3. 32bit per-CPU inter-processor interrupt registers
>
> Unlike other timer devices, CLINT provides IPI registers along with
> timer registers. To use CLINT IPI registers, the CLINT timer driver
> provides IPI related callbacks to arch/riscv.
>
> Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> Tested-by: Emil Renner Berhing <kernel@xxxxxxxx>
> ---
> drivers/clocksource/Kconfig | 9 ++
> drivers/clocksource/Makefile | 1 +
> drivers/clocksource/timer-clint.c | 231 ++++++++++++++++++++++++++++++
> include/linux/cpuhotplug.h | 1 +
> 4 files changed, 242 insertions(+)
> create mode 100644 drivers/clocksource/timer-clint.c
>
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 91418381fcd4..e1ce0d510a03 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -658,6 +658,15 @@ config RISCV_TIMER
> is accessed via both the SBI and the rdcycle instruction. This is
> required for all RISC-V systems.
>
> +config CLINT_TIMER
> + bool "Timer for the RISC-V platform"
> + depends on GENERIC_SCHED_CLOCK && RISCV_M_MODE
> + select TIMER_PROBE
> + select TIMER_OF
> + help
> + This option enables the CLINT timer for RISC-V systems. The CLINT
> + driver is usually used for NoMMU RISC-V systems.
V3 has a comment about fixing the Kconfig option.
[ ... ]
> +{
> + bool *registered = per_cpu_ptr(&clint_clock_event_registered, cpu);
> + struct clock_event_device *ce = per_cpu_ptr(&clint_clock_event, cpu);
> +
> + if (!(*registered)) {
> + ce->cpumask = cpumask_of(cpu);
> + clockevents_config_and_register(ce, clint_timer_freq, 200,
> + ULONG_MAX);
> + *registered = true;
> + }
I was unsure about the clockevents_config_and_register() multiple calls
when doing the comment. It seems like it is fine to call it several
times and that is done in several places like riscv or arch_arm_timer.
It is probably safe to drop the 'registered' code here, sorry for the
confusion.
> + enable_percpu_irq(clint_timer_irq,
> + irq_get_trigger_type(clint_timer_irq));
> + return 0;
> +}
> +
[ ... ]
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