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

[Daniel Lezcano <daniel.lezcano@linaro.org>]

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);
>>>
>>
>>
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