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

Daniel Lezcano
2018-11-05T11:48:19Z

Hi Clément,

On 04/11/2018 17:07, Clément Péron wrote:
> Hi Daniel,
>
> Thanks for the review and sorry for the delay.

no problem.

> On Tue, 10 Jul 2018 at 18:20, Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>>
>> On 11/06/2018 17:50, Clément Péron wrote:
>>> From: Colin Didier <colin.didier@devialet.com>
>>>
>>> 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@devialet.com>
>>> Signed-off-by: Clément Peron <clement.peron@devialet.com>
>>> Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
>>> Tested-by: Vladimir Zapolskiy <vz@mleia.com>
>>> ---
>>> 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@pengutronix.de>
>>> + * Copyright (C) 2018 Colin Didier <colin.didier@devialet.com>
>>> + * Copyright (C) 2018 Clément Péron <clement.peron@devialet.com>
>>> + */
>>> +
>>> +#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 ?

Yes, the pointed code is 10 years old, so if you are willing to do the
changes in a separate patchset, that would be nice.

>>> + /* 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

If we reach this point of code with a pending timer interrupt, that
means it should be processed after the clockevent shutdown path is
finished. Otherwise it is like we cancel the timer on the back of the
system.

>> 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);
>>>
>>
>>
>> --
>> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
>>
>> Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
>> <http://twitter.com/#!/linaroorg> Twitter |
>> <http://www.linaro.org/linaro-blog/> Blog
>>

--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |