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SubjectRE: [PATCH v2 2/2] driver: clocksource: Add nxp system counter timer driver support
Date
> Subject: Re: [PATCH v2 2/2] driver: clocksource: Add nxp system counter timer
> driver support
>
> On 12/12/2018 06:28, Jacky Bai wrote:
> > The system counter (sys_ctr) is a programmable system counter which
> > provides a shared time base to the Cortex A15, A7, A53 etc cores.
> > It is intended for use in applications where the counter is always
> > powered on and supports multiple, unrelated clocks. The sys_ctr
> > hardware
> > supports:
> > - 56-bit counter width (roll-over time greater than 40 years)
> > - compare frame(64-bit compare value) contains programmable interrupt
> > generation
> >
> > Signed-off-by: Bai Ping <ping.bai@nxp.com>
> > ---
> > change v1->v2:
> > - no change
> > ---
> > drivers/clocksource/Kconfig | 8 ++
> > drivers/clocksource/Makefile | 1 +
> > drivers/clocksource/timer-imx-sysctr.c | 204
> > +++++++++++++++++++++++++++++++++
> > 3 files changed, 213 insertions(+)
> > create mode 100644 drivers/clocksource/timer-imx-sysctr.c
> >
> > diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> > index c57b156..7e5f2de 100644
> > --- a/drivers/clocksource/Kconfig
> > +++ b/drivers/clocksource/Kconfig
> > @@ -579,6 +579,14 @@ config CLKSRC_IMX_TPM
> > Enable this option to use IMX Timer/PWM Module (TPM) timer as
> > clocksource.
> >
> > +config CLKSRC_IMX_SYS_CTR
>
> As the driver is a timer, please replace the CLKSRC by TIMER

Ok, will fix it.

>
> > + bool "Clocksource using i.MX system counter" if COMPILE_TEST
> > + depends on (ARM || ARM64) && CLKDEV_LOOKUP
>
> CLKDEV_LOOKUP is not needed, it is selected with COMMON_CLK
>
> > + select CLKSRC_MMIO
> > + help
> > + Enable this option to use IMX system counter timer as
> > + clocksource.
> > +
> > config CLKSRC_ST_LPC
> > bool "Low power clocksource found in the LPC" if COMPILE_TEST
> > select TIMER_OF if OF
> > diff --git a/drivers/clocksource/Makefile
> > b/drivers/clocksource/Makefile index dd91381..372bf4e 100644
> > --- a/drivers/clocksource/Makefile
> > +++ b/drivers/clocksource/Makefile
> > @@ -71,6 +71,7 @@ obj-$(CONFIG_CLKSRC_MIPS_GIC) +=
> mips-gic-timer.o
> > obj-$(CONFIG_CLKSRC_TANGO_XTAL) += tango_xtal.o
> > obj-$(CONFIG_CLKSRC_IMX_GPT) += timer-imx-gpt.o
> > obj-$(CONFIG_CLKSRC_IMX_TPM) += timer-imx-tpm.o
> > +obj-$(CONFIG_CLKSRC_IMX_SYS_CTR) += timer-imx-sysctr.o
> > obj-$(CONFIG_ASM9260_TIMER) += asm9260_timer.o
> > obj-$(CONFIG_H8300_TMR8) += h8300_timer8.o
> > obj-$(CONFIG_H8300_TMR16) += h8300_timer16.o
> > diff --git a/drivers/clocksource/timer-imx-sysctr.c
> > b/drivers/clocksource/timer-imx-sysctr.c
> > new file mode 100644
> > index 0000000..ad3c27f
> > --- /dev/null
> > +++ b/drivers/clocksource/timer-imx-sysctr.c
> > @@ -0,0 +1,204 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +//
> > +// Copyright 2017-2018 NXP
> > +
> > +#include <linux/interrupt.h>
> > +#include <linux/clockchips.h>
> > +#include <linux/clocksource.h>
> > +#include <linux/delay.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_irq.h>
> > +#include <linux/sched_clock.h>
> > +
> > +#define CNTCV_LO 0x8
> > +#define CNTCV_HI 0xc
> > +#define CMPCV_LO 0x20
> > +#define CMPCV_HI 0x24
> > +#define CMPCR 0x2c
> > +
> > +#define SYS_CTR_EN 0x1
> > +#define SYS_CTR_IRQ_MASK 0x2
> > +
> > +static void __iomem *sys_ctr_rd_base; static void __iomem
> > +*sys_ctr_cmp_base; static struct clock_event_device
> > +clockevent_sysctr;
> > +
> > +static inline void sysctr_timer_enable(bool enable)
>
> Remove 'inline' tag
>

OK.

> > +{
> > + u32 val;
> > +
> > + val = readl(sys_ctr_cmp_base + CMPCR);
> > + val &= ~SYS_CTR_EN;
> > + if (enable)
> > + val |= SYS_CTR_EN;
> > +
> > + writel(val, sys_ctr_cmp_base + CMPCR); }
> > +
> > +static void sysctr_irq_acknowledge(void) {
> > + u32 val;
> > +
> > + /* clear th enable bit(EN=0) to clear the ISTAT */
>
> What is the ISTAT?
>
> Thanks for adding comments, however the format is:
>
> /*
> *
> */
>

Th ISTAT is interrupt status bit. I will fix it.

> > + val = readl(sys_ctr_cmp_base + CMPCR);
> > + val &= ~SYS_CTR_EN;
> > + writel(val, sys_ctr_cmp_base + CMPCR);
>
> This is duplicate with the sysctr_timer_enable() function, call it instead of
> duplicating code.
>
Sure.

> > +}
> > +
> > +static inline u64 sysctr_read_counter(void) {
> > + u32 cnt_hi, tmp_hi, cnt_lo;
> > +
> > + do {
> > + cnt_hi = readl_relaxed(sys_ctr_rd_base + CNTCV_HI);
> > + cnt_lo = readl_relaxed(sys_ctr_rd_base + CNTCV_LO);
> > + tmp_hi = readl_relaxed(sys_ctr_rd_base + CNTCV_HI);
> > + } while (tmp_hi != cnt_hi);
> > +
> > + return ((u64) cnt_hi << 32) | cnt_lo; }
>
> It has been showed a 64bit counter usage adds a non negligible overhead,
> especially on 32bits. Are you really sure you want this ?
>

This HW is designed as 56 bit counter & timer. when doing timer 'set_next_event',
The 56bit counter value must be read out, and then adding the delta value to set the
next event. Can you give me some suggestion on how to handle this?

> > +static u64 notrace sysctr_read_sched_clock(void) {
> > + return sysctr_read_counter();
> > +}
> > +
> > +static u64 sysctr_clocksource_read(struct clocksource *cs) {
> > + return sysctr_read_counter();
> > +}
> > +
> > +static int __init sysctr_clocksource_init(unsigned int rate) {
> > + sched_clock_register(sysctr_read_sched_clock, 56, rate);
> > + return clocksource_mmio_init(sys_ctr_rd_base, "i.MX sys_ctr",
> > + rate, 200, 56, sysctr_clocksource_read); }
> > +
> > +static int sysctr_set_next_event(unsigned long delta,
> > + struct clock_event_device *evt)
> > +{
> > + u32 cmp_hi, cmp_lo;
> > + u64 next;
> > +
> > + sysctr_timer_enable(false);
> > +
> > + next = sysctr_read_counter();
> > +
> > + next += delta;
> > +
> > + cmp_hi = (next >> 32) & 0x00fffff;
> > + cmp_lo = next & 0xffffffff;
> > +
> > + writel_relaxed(cmp_hi, sys_ctr_cmp_base + CMPCV_HI);
> > + writel_relaxed(cmp_lo, sys_ctr_cmp_base + CMPCV_LO);
> > +
> > + sysctr_timer_enable(true);
> > +
> > + return 0;
> > +}
> > +
> > +static int sysctr_set_state_oneshot(struct clock_event_device *evt) {
> > + /* enable timer */
>
> The function name is explicit enough, no need to add this comment
>

OK, will remove it in V3.

> > + sysctr_timer_enable(true);
> > +
> > + return 0;
> > +}
> > +
> > +static int sysctr_set_state_shutdown(struct clock_event_device *evt)
> > +{
> > + /* disable the timer */
>
> Ditto
>
> > + sysctr_timer_enable(false);
> > +
> > + return 0;
> > +}
> > +
> > +static irqreturn_t sysctr_timer_interrupt(int irq, void *dev_id) {
> > + struct clock_event_device *evt = &clockevent_sysctr;
> > +
> > + sysctr_irq_acknowledge();
> > +
> > + evt->event_handler(evt);
> > +
> > + return IRQ_HANDLED;
> > +}
> > +
> > +static struct clock_event_device clockevent_sysctr = {
> > + .name = "i.MX system counter timer",
> > + .features = CLOCK_EVT_FEAT_ONESHOT |
> CLOCK_EVT_FEAT_DYNIRQ,
> > + .set_state_oneshot = sysctr_set_state_oneshot,
> > + .set_next_event = sysctr_set_next_event,
> > + .set_state_shutdown = sysctr_set_state_shutdown,
> > + .rating = 200,
> > +};
> > +
> > +static int __init sysctr_clockevent_init(unsigned long rate, int irq)
> > +{
> > + int ret;
> > +
> > + ret = request_irq(irq, sysctr_timer_interrupt, IRQF_TIMER |
> IRQF_IRQPOLL,
> > + "i.MX system counter timer", &clockevent_sysctr);
> > + if (ret) {
> > + pr_err("Failed to request i.MX sysctr timer irq\n");
> > + return ret;
> > + }
> > +
> > + clockevent_sysctr.cpumask = cpumask_of(0);
> > + clockevent_sysctr.irq = irq;
> > + clockevents_config_and_register(&clockevent_sysctr,
> > + rate, 0xff, 0x7fffffff);
> > + return 0;
> > +}
> > +
> > +static int __init sysctr_timer_init(struct device_node *np) {
> > + u32 rate;
> > + int irq, ret = 0;
> > +
> > + /* map the system counter's CNTreadbase */
>
> Comment not useful, remove it
>
> > + sys_ctr_rd_base = of_iomap(np, 0);
> > + if (!sys_ctr_rd_base) {
> > + pr_err("Failed to map sys_ctr rd base%pOF\n", np);
>
> nit: space missing after 'base'
>
> > + return -ENXIO;
> > + }
> > +
> > + /* map the system counter's CNTcomparebase */
>
> Remove comment
>
> > + sys_ctr_cmp_base = of_iomap(np, 1);
> > + if (!sys_ctr_cmp_base) {
> > + pr_err("Failed to map sys_ctr compare base%pOF\n", np);
> > + ret = -ENXIO;
> > + goto out_free2;
> > + }
> > +
> > + /*
> > + * the purpose of this driver is to provide a global timer,
> > + * So only use one compare frame, request frame0's irq only.
> > + */
> > + irq = irq_of_parse_and_map(np, 0);
> > + if (!irq) {
> > + pr_err("Failed to map interrupt for %pOF\n", np);
> > + ret = -EINVAL;
> > + goto out_free1;
> > + }
> > +
> > + if (of_property_read_u32(np, "clock-frequency", &rate)) {
> > + pr_err("Failed to get clock frequency %pOF\n", np);
> > + ret = -EINVAL;
> > + goto out_free1;
> > + }
>
> Please replace it with a 'fixed-clock' in the DT and use the clk API.
>
> In addition you can use the timer-of API (cf timer-of.h)
>

Thanks, I will fix it in V3.

> > +
> > + sysctr_clocksource_init(rate);
> > + sysctr_clockevent_init(rate, irq);
> > +
> > + return 0;
> > +
> > +out_free1:
>
> label names are inadequate, use out_iounmap_cmp: for example
>

Will fix it in V3.

BR

> > + iounmap(sys_ctr_cmp_base);
> > +out_free2:
> > + iounmap(sys_ctr_rd_base);
> > + return ret;
> > +}
> > +TIMER_OF_DECLARE(sysctr_timer, "nxp,sysctr-timer",
> > +sysctr_timer_init);
> >

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