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Subject: Re: [PATCH v2 2/2] driver: clocksource: Add nxp system counter timer
 driver support
To:     Jacky Bai <ping.bai@nxp.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        Aisheng Dong <aisheng.dong@nxp.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>
References: <1544592770-19996-1-git-send-email-ping.bai@nxp.com>
 <1544592770-19996-2-git-send-email-ping.bai@nxp.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <d38cda5d-b78b-10de-2c19-be5fd869243a@linaro.org>
Date:   Mon, 14 Jan 2019 16:45:19 +0100
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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

> +	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

> +{
> +	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:

/*
 *
 */

> +	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.

> +}
> +
> +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 ?

> +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

> +	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)

> +
> +	sysctr_clocksource_init(rate);
> +	sysctr_clockevent_init(rate, irq);
> +
> +	return 0;
> +
> +out_free1:

label names are inadequate, use out_iounmap_cmp: for example

> +	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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