Re: [PATCH v7 4/5] clocksource: add driver for i.MX EPIT timer

From: ClÃment PÃron
Date: Sun Nov 04 2018 - 11:08:02 EST

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Hi Daniel,

Thanks for the review and sorry for the delay.

On Tue, 10 Jul 2018 at 18:20, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote:
>
> On 11/06/2018 17:50, ClÃment PÃron wrote:
> > From: Colin Didier <colin.didier@xxxxxxxxxxxx>
> >
> > Add driver for NXP's EPIT timer used in i.MX SoC.
>
> Give a description on how works this timer.
Ok,

>
>
> > Signed-off-by: Colin Didier <colin.didier@xxxxxxxxxxxx>
> > Signed-off-by: ClÃment Peron <clement.peron@xxxxxxxxxxxx>
> > Reviewed-by: Vladimir Zapolskiy <vz@xxxxxxxxx>
> > Tested-by: Vladimir Zapolskiy <vz@xxxxxxxxx>
> > ---
> > drivers/clocksource/Kconfig | 11 ++
> > drivers/clocksource/Makefile | 1 +
> > drivers/clocksource/timer-imx-epit.c | 265 +++++++++++++++++++++++++++
> > 3 files changed, 277 insertions(+)
> > create mode 100644 drivers/clocksource/timer-imx-epit.c
> >
> > diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> > index 8e8a09755d10..790478afd02c 100644
> > --- a/drivers/clocksource/Kconfig
> > +++ b/drivers/clocksource/Kconfig
> > @@ -576,6 +576,17 @@ config H8300_TPU
> > This enables the clocksource for the H8300 platform with the
> > H8S2678 cpu.
> >
> > +config CLKSRC_IMX_EPIT
> > + bool "Clocksource using i.MX EPIT"
> > + depends on CLKDEV_LOOKUP && (ARCH_MXC || COMPILE_TEST)
> > + select CLKSRC_MMIO
> > + help
> > + This enables EPIT support available on some i.MX platforms.
> > + Normally you don't have a reason to do so as the EPIT has
> > + the same features and uses the same clocks as the GPT.
> > + Anyway, on some systems the GPT may be in use for other
> > + purposes.
> > +
> > config CLKSRC_IMX_GPT
> > bool "Clocksource using i.MX GPT" if COMPILE_TEST
> > depends on ARM && CLKDEV_LOOKUP
> > diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> > index 00caf37e52f9..d9426f69ec69 100644
> > --- a/drivers/clocksource/Makefile
> > +++ b/drivers/clocksource/Makefile
> > @@ -69,6 +69,7 @@ obj-$(CONFIG_INTEGRATOR_AP_TIMER) += timer-integrator-ap.o
> > obj-$(CONFIG_CLKSRC_VERSATILE) += versatile.o
> > obj-$(CONFIG_CLKSRC_MIPS_GIC) += mips-gic-timer.o
> > obj-$(CONFIG_CLKSRC_TANGO_XTAL) += tango_xtal.o
> > +obj-$(CONFIG_CLKSRC_IMX_EPIT) += timer-imx-epit.o
> > obj-$(CONFIG_CLKSRC_IMX_GPT) += timer-imx-gpt.o
> > obj-$(CONFIG_CLKSRC_IMX_TPM) += timer-imx-tpm.o
> > obj-$(CONFIG_ASM9260_TIMER) += asm9260_timer.o
> > diff --git a/drivers/clocksource/timer-imx-epit.c b/drivers/clocksource/timer-imx-epit.c
> > new file mode 100644
> > index 000000000000..7f1c8e2e00aa
> > --- /dev/null
> > +++ b/drivers/clocksource/timer-imx-epit.c
> > @@ -0,0 +1,265 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * i.MX EPIT Timer
> > + *
> > + * Copyright (C) 2010 Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> > + * Copyright (C) 2018 Colin Didier <colin.didier@xxxxxxxxxxxx>
> > + * Copyright (C) 2018 ClÃment PÃron <clement.peron@xxxxxxxxxxxx>
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/clockchips.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_irq.h>
> > +#include <linux/sched_clock.h>
> > +#include <linux/slab.h>
> > +
> > +#define EPITCR 0x00
> > +#define EPITSR 0x04
> > +#define EPITLR 0x08
> > +#define EPITCMPR 0x0c
> > +#define EPITCNR 0x10
> > +
> > +#define EPITCR_EN BIT(0)
> > +#define EPITCR_ENMOD BIT(1)
> > +#define EPITCR_OCIEN BIT(2)
> > +#define EPITCR_RLD BIT(3)
> > +#define EPITCR_PRESC(x) (((x) & 0xfff) << 4)
> > +#define EPITCR_SWR BIT(16)
> > +#define EPITCR_IOVW BIT(17)
> > +#define EPITCR_DBGEN BIT(18)
> > +#define EPITCR_WAITEN BIT(19)
> > +#define EPITCR_RES BIT(20)
> > +#define EPITCR_STOPEN BIT(21)
> > +#define EPITCR_OM_DISCON (0 << 22)
> > +#define EPITCR_OM_TOGGLE (1 << 22)
> > +#define EPITCR_OM_CLEAR (2 << 22)
> > +#define EPITCR_OM_SET (3 << 22)
> > +#define EPITCR_CLKSRC_OFF (0 << 24)
> > +#define EPITCR_CLKSRC_PERIPHERAL (1 << 24)
> > +#define EPITCR_CLKSRC_REF_HIGH (2 << 24)
> > +#define EPITCR_CLKSRC_REF_LOW (3 << 24)
> > +
> > +#define EPITSR_OCIF BIT(0)
> > +
> > +struct epit_timer {
> > + void __iomem *base;
> > + int irq;
> > + struct clk *clk;
> > + struct clock_event_device ced;
> > + struct irqaction act;
> > +};
> > +
> > +static void __iomem *sched_clock_reg;
> > +
> > +static inline struct epit_timer *to_epit_timer(struct clock_event_device *ced)
> > +{
> > + return container_of(ced, struct epit_timer, ced);
> > +}
> > +
> > +static inline void epit_irq_disable(struct epit_timer *epittm)
> > +{
> > + u32 val;
> > +
> > + val = readl_relaxed(epittm->base + EPITCR);
> > + writel_relaxed(val & ~EPITCR_OCIEN, epittm->base + EPITCR);
> > +}
> > +
> > +static inline void epit_irq_enable(struct epit_timer *epittm)
> > +{
> > + u32 val;
> > +
> > + val = readl_relaxed(epittm->base + EPITCR);
> > + writel_relaxed(val | EPITCR_OCIEN, epittm->base + EPITCR);
> > +}
> > +
> > +static void epit_irq_acknowledge(struct epit_timer *epittm)
> > +{
> > + writel_relaxed(EPITSR_OCIF, epittm->base + EPITSR);
> > +}
> > +
> > +static u64 notrace epit_read_sched_clock(void)
> > +{
> > + return ~readl_relaxed(sched_clock_reg);
> > +}
> > +
> > +static int epit_set_next_event(unsigned long cycles,
> > + struct clock_event_device *ced)
> > +{
> > + struct epit_timer *epittm = to_epit_timer(ced);
> > + unsigned long tcmp;
> > +
> > + tcmp = readl_relaxed(epittm->base + EPITCNR) - cycles;
> > + writel_relaxed(tcmp, epittm->base + EPITCMPR);
> > +
> > + return 0;
> > +}
> > +
> > +/* Left event sources disabled, no more interrupts appear */
> > +static int epit_shutdown(struct clock_event_device *ced)
> > +{
> > + struct epit_timer *epittm = to_epit_timer(ced);
> > + unsigned long flags;
> > +
> > + /*
> > + * The timer interrupt generation is disabled at least
> > + * for enough time to call epit_set_next_event()
> > + */
> > + local_irq_save(flags);
>
> This is not necessary. This function is called with interrupt disabled.

I took this from the i.MX GPT Timer :
https://elixir.bootlin.com/linux/latest/source/drivers/clocksource/timer-imx-gpt.c#L208

Do you think i should also fix on the imx gpt timer ?

>
> > + /* Disable interrupt in EPIT module */
> > + epit_irq_disable(epittm);
> > +
> > + /* Clear pending interrupt */
> > + epit_irq_acknowledge(epittm);
>
> No irq ack is needed here. Neither disabling the interrupt.
Is it done by the framework ?

I took also this from the IMX GPT driver

>
> Why not just stop the counter ?
I will check the datasheet.
>
> > + local_irq_restore(flags);
> > +
> > + return 0;
> > +}
> > +
> > +static int epit_set_oneshot(struct clock_event_device *ced)
> > +{
> > + struct epit_timer *epittm = to_epit_timer(ced);
> > + unsigned long flags;
> > +
> > + /*
> > + * The timer interrupt generation is disabled at least
> > + * for enough time to call epit_set_next_event()
> > + */
> > + local_irq_save(flags);
>
> This is not necessary. This function is called with interrupt disabled.
>
> > + /* Disable interrupt in EPIT module */
> > + epit_irq_disable(epittm);
> > +
> > + /* Clear pending interrupt, only while switching mode */
> > + if (!clockevent_state_oneshot(ced))
> > + epit_irq_acknowledge(epittm);
>
> Why do you need to ack the interrupt here ?
>
> > + /*
> > + * Do not put overhead of interrupt enable/disable into
> > + * epit_set_next_event(), the core has about 4 minutes
> > + * to call epit_set_next_event() or shutdown clock after
> > + * mode switching
> > + */
> > + epit_irq_enable(epittm);
> > + local_irq_restore(flags);
> > +
> > + return 0;
> > +}
> > +
> > +static irqreturn_t epit_timer_interrupt(int irq, void *dev_id)
> > +{
> > + struct clock_event_device *ced = dev_id;
> > + struct epit_timer *epittm = to_epit_timer(ced);
> > +
> > + epit_irq_acknowledge(epittm);
> > +
> > + ced->event_handler(ced);
> > +
> > + return IRQ_HANDLED;
> > +}
> > +
> > +static int __init epit_clocksource_init(struct epit_timer *epittm)
> > +{
> > + unsigned int c = clk_get_rate(epittm->clk);
> > +
> > + sched_clock_reg = epittm->base + EPITCNR;
> > + sched_clock_register(epit_read_sched_clock, 32, c);
> > +
> > + return clocksource_mmio_init(epittm->base + EPITCNR, "epit", c, 200, 32,
> > + clocksource_mmio_readl_down);
> > +}
> > +
> > +static int __init epit_clockevent_init(struct epit_timer *epittm)
> > +{
> > + struct clock_event_device *ced = &epittm->ced;
> > + struct irqaction *act = &epittm->act;
> > +
> > + ced->name = "epit";
> > + ced->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_DYNIRQ;
> > + ced->set_state_shutdown = epit_shutdown;
> > + ced->tick_resume = epit_shutdown;
> > + ced->set_state_oneshot = epit_set_oneshot;
> > + ced->set_next_event = epit_set_next_event;
> > + ced->rating = 200;
> > + ced->cpumask = cpumask_of(0);
> > + ced->irq = epittm->irq;
> > + clockevents_config_and_register(ced, clk_get_rate(epittm->clk),
> > + 0xff, 0xfffffffe);
> > +
> > + act->name = "i.MX EPIT Timer Tick",
> > + act->flags = IRQF_TIMER | IRQF_IRQPOLL;
> > + act->handler = epit_timer_interrupt;
> > + act->dev_id = ced;
> > +
> > + /* Make irqs happen */
> > + return setup_irq(epittm->irq, act);
> > +}
> > +
> > +static int __init epit_timer_init(struct device_node *np)
> > +{
> > + struct epit_timer *epittm;
> > + int ret;
> > +
> > + epittm = kzalloc(sizeof(*epittm), GFP_KERNEL);
> > + if (!epittm)
> > + return -ENOMEM;
> > +
> > + epittm->base = of_iomap(np, 0);
> > + if (!epittm->base) {
> > + ret = -ENXIO;
> > + goto out_kfree;
> > + }
> > +
> > + epittm->irq = irq_of_parse_and_map(np, 0);
> > + if (!epittm->irq) {
> > + ret = -EINVAL;
> > + goto out_iounmap;
> > + }
> > +
> > + /* Get EPIT clock */
> > + epittm->clk = of_clk_get(np, 0);
> > + if (IS_ERR(epittm->clk)) {
> > + pr_err("i.MX EPIT: unable to get clk\n");
> > + ret = PTR_ERR(epittm->clk);
> > + goto out_iounmap;
> > + }
> > +
> > + ret = clk_prepare_enable(epittm->clk);
> > + if (ret) {
> > + pr_err("i.MX EPIT: unable to prepare+enable clk\n");
> > + goto out_iounmap;
> > + }
>
> Please replace all the above with the timer-of API as:
Ok I will,

Thanks
Clement

>
> https://patchwork.kernel.org/patch/10510443/
>
>
> > + /* Initialise to a known state (all timers off, and timing reset) */
> > + writel_relaxed(0x0, epittm->base + EPITCR);
> > + writel_relaxed(0xffffffff, epittm->base + EPITLR);
> > + writel_relaxed(EPITCR_EN | EPITCR_CLKSRC_REF_HIGH | EPITCR_WAITEN,
> > + epittm->base + EPITCR);
> > +
> > + ret = epit_clocksource_init(epittm);
> > + if (ret) {
> > + pr_err("i.MX EPIT: failed to init clocksource\n");
> > + goto out_clk_disable;
> > + }
> > +
> > + ret = epit_clockevent_init(epittm);
> > + if (ret) {
> > + pr_err("i.MX EPIT: failed to init clockevent\n");
> > + goto out_clk_disable;
> > + }
> > +
> > + return 0;
> > +
> > +out_clk_disable:
> > + clk_disable_unprepare(epittm->clk);
> > +out_iounmap:
> > + iounmap(epittm->base);
> > +out_kfree:
> > + kfree(epittm);
> > +
> > + return ret;
> > +}
> > +TIMER_OF_DECLARE(epit_timer, "fsl,imx31-epit", epit_timer_init);
> >
>
>
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