Re: [PATCH v2 3/3] clocksource: Add clockevent support to NPS400 driver

Daniel Lezcano
2016-10-31T10:53:00Z

On Sun, Oct 23, 2016 at 03:12:28PM +0300, Noam Camus wrote:
> From: Noam Camus <noamca@mellanox.com>
>
> Till now we used clockevent from generic ARC driver.
> This was enough as long as we worked with simple multicore SoC.
> When we are working with multithread SoC each HW thread can be
> scheduled to receive timer interrupt using timer mask register.
> This patch will provide a way to control clock events per HW thread.
>
> The design idea is that for each core there is dedicated regirtser

s/regirtser/register/

Hey ! re-read yourself.

> (TSI) serving all 16 HW threads.
> The register is a bitmask with one bit for each HW thread.
> When HW thread wants that next expiration of timer interrupt will
> hit it then the proper bit should be set in this dedicated register.

I'm not sure to understand this sentence. Do you mean each cpu/thread must
set a flag in the TSI register at BIT(phys_id) when they set a timer ?

> When timer expires all HW threads within this core which their bit
> is set at the TSI register will be interrupted.

Does it mean some HW threads will be wake up for nothing ?

eg.

HWT1 sets the timer to expire within 2 seconds
HWT2 sets the timer to expire within 2 hours

When the first timer expires, that will wake up HWT1 *and* HWT2 ?

The code is a bit confusing because of the very specific design of this timer.

Below more questions for clarification.

> Driver can be used from device tree by:
> compatible = "ezchip,nps400-timer0" <-- for clocksource
> compatible = "ezchip,nps400-timer1" <-- for clockevent
>
> Note that name convention for timer0/timer1 was taken from legacy
> ARC design. This design is our base before adding HW threads.
>
> Signed-off-by: Noam Camus <noamca@mellanox.com>
>
> Change-Id: Ib351e6fc7a6b691293040ae655f202f3cc2c1298
> ---
> .../bindings/timer/ezchip,nps400-timer.txt | 15 --
> .../bindings/timer/ezchip,nps400-timer0.txt | 17 ++
> .../bindings/timer/ezchip,nps400-timer1.txt | 15 ++
> drivers/clocksource/timer-nps.c | 220 +++++++++++++++++++-
> include/linux/cpuhotplug.h | 1 +
> 5 files changed, 248 insertions(+), 20 deletions(-)
> delete mode 100644 Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt
> create mode 100644 Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt
> create mode 100644 Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt
>
> diff --git a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt
> deleted file mode 100644
> index c8c03d7..0000000
> --- a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt
> +++ /dev/null
> @@ -1,15 +0,0 @@
> -NPS Network Processor
> -
> -Required properties:
> -
> -- compatible : should be "ezchip,nps400-timer"
> -
> -Clocks required for compatible = "ezchip,nps400-timer":
> -- clocks : Must contain a single entry describing the clock input
> -
> -Example:
> -
> -timer {
> - compatible = "ezchip,nps400-timer";
> - clocks = <&sysclk>;
> -};
> diff --git a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt
> new file mode 100644
> index 0000000..e3cfce8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt
> @@ -0,0 +1,17 @@
> +NPS Network Processor
> +
> +Required properties:
> +
> +- compatible : should be "ezchip,nps400-timer0"
> +
> +Clocks required for compatible = "ezchip,nps400-timer0":
> +- interrupts : The interrupt of the first timer
> +- clocks : Must contain a single entry describing the clock input
> +
> +Example:
> +
> +timer {
> + compatible = "ezchip,nps400-timer0";
> + interrupts = <3>;
> + clocks = <&sysclk>;
> +};
> diff --git a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt
> new file mode 100644
> index 0000000..c0ab419
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt
> @@ -0,0 +1,15 @@
> +NPS Network Processor
> +
> +Required properties:
> +
> +- compatible : should be "ezchip,nps400-timer1"
> +
> +Clocks required for compatible = "ezchip,nps400-timer1":
> +- clocks : Must contain a single entry describing the clock input
> +
> +Example:
> +
> +timer {
> + compatible = "ezchip,nps400-timer1";
> + clocks = <&sysclk>;
> +};
> diff --git a/drivers/clocksource/timer-nps.c b/drivers/clocksource/timer-nps.c
> index 6156e54..0757328 100644
> --- a/drivers/clocksource/timer-nps.c
> +++ b/drivers/clocksource/timer-nps.c
> @@ -46,7 +46,7 @@
> /* This array is per cluster of CPUs (Each NPS400 cluster got 256 CPUs) */
> static void *nps_msu_reg_low_addr[NPS_CLUSTER_NUM] __read_mostly;
>
> -static unsigned long nps_timer_rate;
> +static unsigned long nps_timer1_freq;

Why declare a global static variable for a local use in nps_setup_clocksource ?

> static int nps_get_timer_clk(struct device_node *node,
> unsigned long *timer_freq,
> struct clk *clk)
> @@ -87,10 +87,10 @@ static int __init nps_setup_clocksource(struct device_node *node)
> nps_host_reg((cluster << NPS_CLUSTER_OFFSET),
> NPS_MSU_BLKID, NPS_MSU_TICK_LOW);
>
> - nps_get_timer_clk(node, &nps_timer_rate, clk);
> + nps_get_timer_clk(node, &nps_timer1_freq, clk);
>
> - ret = clocksource_mmio_init(nps_msu_reg_low_addr, "EZnps-tick",
> - nps_timer_rate, 301, 32, nps_clksrc_read);
> + ret = clocksource_mmio_init(nps_msu_reg_low_addr, "nps-tick",
> + nps_timer1_freq, 301, 32, nps_clksrc_read);
> if (ret) {
> pr_err("Couldn't register clock source.\n");
> clk_disable_unprepare(clk);
> @@ -99,5 +99,215 @@ static int __init nps_setup_clocksource(struct device_node *node)
> return ret;
> }
>
> -CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clksrc, "ezchip,nps400-timer",
> +CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clksrc, "ezchip,nps400-timer1",
> nps_setup_clocksource);
> +
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +#include <soc/nps/mtm.h>
> +
> +/* Timer related Aux registers */
> +#define AUX_REG_TIMER0_TSI 0xFFFFF850 /* timer 0 HW threads mask */
> +#define NPS_REG_TIMER0_LIMIT 0x23 /* timer 0 limit */
> +#define NPS_REG_TIMER0_CTRL 0x22 /* timer 0 control */
> +#define NPS_REG_TIMER0_CNT 0x21 /* timer 0 count */
> +
> +#define TIMER0_CTRL_IE (1 << 0) /* Interrupt when Count reaches limit */
> +#define TIMER0_CTRL_NH (1 << 1) /* Count only when CPU NOT halted */

Please, use BIT(nr) macro.

Can you elaborate "Count only when CPU NOT halted" ?

> +static unsigned long nps_timer0_freq;
> +static unsigned long nps_timer0_irq;
> +
> +/*
> + * Arm the timer to interrupt after @cycles
> + */
> +static void nps_clkevent_timer_event_setup(unsigned int cycles)
> +{
> + write_aux_reg(NPS_REG_TIMER0_LIMIT, cycles);
> + write_aux_reg(NPS_REG_TIMER0_CNT, 0); /* start from 0 */
> +
> + write_aux_reg(NPS_REG_TIMER0_CTRL, TIMER0_CTRL_IE | TIMER0_CTRL_NH);
> +}
> +
> +static void nps_clkevent_rm_thread(bool remove_thread)
> +{
> + unsigned int cflags;
> + unsigned int enabled_threads;
> + unsigned long flags;
> + int thread;
> +
> + local_irq_save(flags);
> + hw_schd_save(&cflags);

Can you explain why those two lines are needed ?

> + enabled_threads = read_aux_reg(AUX_REG_TIMER0_TSI);
> +
> + /* remove thread from TSI1 */
> + if (remove_thread) {
> + thread = read_aux_reg(CTOP_AUX_THREAD_ID);
> + enabled_threads &= ~(1 << thread);
> + write_aux_reg(AUX_REG_TIMER0_TSI, enabled_threads);
> + }
> +
> + /* Re-arm the timer if needed */
> + if (!enabled_threads)
> + write_aux_reg(NPS_REG_TIMER0_CTRL, TIMER0_CTRL_NH);
> + else
> + write_aux_reg(NPS_REG_TIMER0_CTRL,
> + TIMER0_CTRL_IE | TIMER0_CTRL_NH);
> +
> + hw_schd_restore(cflags);
> + local_irq_restore(flags);
> +}
> +
> +static void nps_clkevent_add_thread(bool set_event)
> +{
> + int thread;
> + unsigned int cflags, enabled_threads;
> + unsigned long flags;
> +
> + local_irq_save(flags);
> + hw_schd_save(&cflags);
> +
> + /* add thread to TSI1 */
> + thread = read_aux_reg(CTOP_AUX_THREAD_ID);
> + enabled_threads = read_aux_reg(AUX_REG_TIMER0_TSI);
> + enabled_threads |= (1 << thread);
> + write_aux_reg(AUX_REG_TIMER0_TSI, enabled_threads);
> +
> + /* set next timer event */
> + if (set_event)
> + write_aux_reg(NPS_REG_TIMER0_CTRL,
> + TIMER0_CTRL_IE | TIMER0_CTRL_NH);
> +
> + hw_schd_restore(cflags);
> + local_irq_restore(flags);
> +}
> +
> +static int nps_clkevent_set_next_event(unsigned long delta,
> + struct clock_event_device *dev)
> +{
> + struct irq_desc *desc = irq_to_desc(nps_timer0_irq);
> + struct irq_chip *chip = irq_data_get_irq_chip(&desc->irq_data);
> +
> + nps_clkevent_add_thread(true);
> + chip->irq_unmask(&desc->irq_data);

Can you explain why invoking low level IRQ callbacks is needed here ?

> + return 0;
> +}
> +
> +/*
> + * Whenever anyone tries to change modes, we just mask interrupts
> + * and wait for the next event to get set.
> + */
> +static int nps_clkevent_timer_shutdown(struct clock_event_device *dev)
> +{
> + struct irq_desc *desc = irq_to_desc(nps_timer0_irq);
> + struct irq_chip *chip = irq_data_get_irq_chip(&desc->irq_data);
> +
> + chip->irq_mask(&desc->irq_data);
> +
> + return 0;
> +}
> +
> +static int nps_clkevent_set_periodic(struct clock_event_device *dev)
> +{
> + nps_clkevent_add_thread(false);
> + if (read_aux_reg(CTOP_AUX_THREAD_ID) == 0)
> + nps_clkevent_timer_event_setup(nps_timer0_freq / HZ);

Please explain this. I read only CPU0 can set the periodic timer.

> + return 0;
> +}
> +
> +static int nps_clkevent_set_oneshot(struct clock_event_device *dev)
> +{
> + nps_clkevent_rm_thread(true);
> + nps_clkevent_timer_shutdown(dev);
> +
> + return 0;
> +}
> +
> +static DEFINE_PER_CPU(struct clock_event_device, nps_clockevent_device) = {
> + .name = "NPS Timer0",
> + .features = CLOCK_EVT_FEAT_ONESHOT |
> + CLOCK_EVT_FEAT_PERIODIC,
> + .rating = 300,
> + .set_next_event = nps_clkevent_set_next_event,
> + .set_state_periodic = nps_clkevent_set_periodic,
> + .set_state_oneshot = nps_clkevent_set_oneshot,
> + .set_state_oneshot_stopped = nps_clkevent_timer_shutdown,
> + .set_state_shutdown = nps_clkevent_timer_shutdown,
> + .tick_resume = nps_clkevent_timer_shutdown,
> +};
> +
> +static irqreturn_t timer_irq_handler(int irq, void *dev_id)
> +{
> + /*
> + * Note that generic IRQ core could have passed @evt for @dev_id if
> + * irq_set_chip_and_handler() asked for handle_percpu_devid_irq()
> + */
> + struct clock_event_device *evt = this_cpu_ptr(&nps_clockevent_device);
> + int irq_reenable = clockevent_state_periodic(evt);
> +
> + nps_clkevent_rm_thread(!irq_reenable);
> +
> + evt->event_handler(evt);
> +
> + return IRQ_HANDLED;
> +}
> +
> +static int nps_timer_starting_cpu(unsigned int cpu)
> +{
> + struct clock_event_device *evt = this_cpu_ptr(&nps_clockevent_device);
> +
> + evt->cpumask = cpumask_of(smp_processor_id());
> +
> + clockevents_config_and_register(evt, nps_timer0_freq, 0, ULONG_MAX);
> + enable_percpu_irq(nps_timer0_irq, 0);
> +
> + return 0;
> +}
> +
> +static int nps_timer_dying_cpu(unsigned int cpu)
> +{
> + disable_percpu_irq(nps_timer0_irq);
> + return 0;
> +}
> +
> +static int __init nps_setup_clockevent(struct device_node *node)
> +{
> + struct clock_event_device *evt = this_cpu_ptr(&nps_clockevent_device);
> + struct clk *clk;

clk = 0xDEADBEEF

> + int ret;
> +
> + nps_timer0_irq = irq_of_parse_and_map(node, 0);
> + if (nps_timer0_irq <= 0) {
> + pr_err("clockevent: missing irq");
> + return -EINVAL;
> + }
> +
> + nps_get_timer_clk(node, &nps_timer0_freq, clk);
> +
> + /* Needs apriori irq_set_percpu_devid() done in intc map function */
> + ret = request_percpu_irq(nps_timer0_irq, timer_irq_handler,
> + "Timer0 (per-cpu-tick)", evt);
> + if (ret) {
> + pr_err("Couldn't request irq\n");
> + clk_disable_unprepare(clk);

clk is on the stack, hence returning back from the function, clk is undefined.

clk_disable_unprepare(0xDEADBEEF) ==> kernel panic

It does not make sense to add the nps_get_timer_clk() function.

Better to have a couple of duplicated lines and properly rollback
from the right place instead of rollbacking supposed actions taken
from inside a function.

> + return ret;
> + }
> +
> + ret = cpuhp_setup_state(CPUHP_AP_NPS_TIMER_STARTING,
> + "AP_NPS_TIMER_STARTING",
> + nps_timer_starting_cpu,
> + nps_timer_dying_cpu);
> + if (ret) {
> + pr_err("Failed to setup hotplug state");
> + clk_disable_unprepare(clk);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clkevt, "ezchip,nps400-timer0",
> + nps_setup_clockevent);
> +#endif /* CONFIG_EZNPS_MTM_EXT */
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 34bd805..9efc1a3 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -60,6 +60,7 @@ enum cpuhp_state {
> CPUHP_AP_MARCO_TIMER_STARTING,
> CPUHP_AP_MIPS_GIC_TIMER_STARTING,
> CPUHP_AP_ARC_TIMER_STARTING,
> + CPUHP_AP_NPS_TIMER_STARTING,

Oops, wait. Here, arch/arc/kernel/time.c should be moved in
drivers/clocksource and consolidated with this driver.

Very likely, CPUHP_AP_ARC_TIMER_STARTING can be used for all ARC
timers.

> CPUHP_AP_KVM_STARTING,
> CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
> CPUHP_AP_KVM_ARM_VGIC_STARTING,
> --
> 1.7.1
>