Re: [PATCH v1 09/43] clocksource: ep93xx: Add driver for Cirrus Logic EP93xx

From: Alexander Sverdlin
Date: Sun Jun 04 2023 - 11:49:47 EST


On Thu, 2023-06-01 at 08:34 +0300, Nikita Shubin wrote:
> This us a rewrite of EP93xx timer driver in
> arch/arm/mach-ep93xx/timer-ep93xx.c trying to do everything
> the device tree way:
>
> - Make every IO-access relative to a base address and dynamic
>   so we can do a dynamic ioremap and get going.
> - Find register range and interrupt from the device tree.
>
> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Signed-off-by: Nikita Shubin <nikita.shubin@xxxxxxxxxxx>

Tested-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>

> ---
>
> Notes:
>     v0 -> v1:
>    
>     - fixed headers
>
>  drivers/clocksource/Kconfig        |  11 ++
>  drivers/clocksource/Makefile       |   1 +
>  drivers/clocksource/timer-ep93xx.c | 189 +++++++++++++++++++++++++++++
>  3 files changed, 201 insertions(+)
>  create mode 100644 drivers/clocksource/timer-ep93xx.c
>
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 5fc8f0e7fb38..40bfc7c86756 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -721,4 +721,15 @@ config GOLDFISH_TIMER
>         help
>           Support for the timer/counter of goldfish-rtc
>  
> +config EP93XX_TIMER
> +       bool "Cirrus Logic ep93xx timer driver" if COMPILE_TEST
> +       depends on ARCH_EP93XX
> +       depends on GENERIC_CLOCKEVENTS
> +       depends on HAS_IOMEM
> +       select CLKSRC_MMIO
> +       select TIMER_OF
> +       help
> +         Enables support for the Cirrus Logic timer block
> +         EP93XX.
> +
>  endmenu
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index 64ab547de97b..09c2d4e5d809 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -88,3 +88,4 @@ obj-$(CONFIG_MICROCHIP_PIT64B)                += timer-microchip-pit64b.o
>  obj-$(CONFIG_MSC313E_TIMER)            += timer-msc313e.o
>  obj-$(CONFIG_GOLDFISH_TIMER)           += timer-goldfish.o
>  obj-$(CONFIG_GXP_TIMER)                        += timer-gxp.o
> +obj-$(CONFIG_EP93XX_TIMER)             += timer-ep93xx.o
> diff --git a/drivers/clocksource/timer-ep93xx.c b/drivers/clocksource/timer-ep93xx.c
> new file mode 100644
> index 000000000000..966502169aa0
> --- /dev/null
> +++ b/drivers/clocksource/timer-ep93xx.c
> @@ -0,0 +1,189 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Cirrus Logic EP93xx timer driver.
> + * Copyright (C) 2021 Nikita Shubin <nikita.shubin@xxxxxxxxxxx>
> + *
> + * Based on a rewrite of arch/arm/mach-ep93xx/timer.c:
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/clocksource.h>
> +#include <linux/clockchips.h>
> +#include <linux/sched_clock.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/of_irq.h>
> +#include <linux/of_address.h>
> +#include <linux/io.h>
> +#include <asm/mach/time.h>
> +
> +/*************************************************************************
> + * Timer handling for EP93xx
> + *************************************************************************
> + * The ep93xx has four internal timers.  Timers 1, 2 (both 16 bit) and
> + * 3 (32 bit) count down at 508 kHz, are self-reloading, and can generate
> + * an interrupt on underflow.  Timer 4 (40 bit) counts down at 983.04 kHz,
> + * is free-running, and can't generate interrupts.
> + *
> + * The 508 kHz timers are ideal for use for the timer interrupt, as the
> + * most common values of HZ divide 508 kHz nicely.  We pick the 32 bit
> + * timer (timer 3) to get as long sleep intervals as possible when using
> + * CONFIG_NO_HZ.
> + *
> + * The higher clock rate of timer 4 makes it a better choice than the
> + * other timers for use as clock source and for sched_clock(), providing
> + * a stable 40 bit time base.
> + *************************************************************************
> + */
> +
> +#define EP93XX_TIMER1_LOAD             0x00
> +#define EP93XX_TIMER1_VALUE            0x04
> +#define EP93XX_TIMER1_CONTROL          0x08
> +#define EP93XX_TIMER123_CONTROL_ENABLE BIT(7)
> +#define EP93XX_TIMER123_CONTROL_MODE   BIT(6)
> +#define EP93XX_TIMER123_CONTROL_CLKSEL BIT(3)
> +#define EP93XX_TIMER1_CLEAR            0x0c
> +#define EP93XX_TIMER2_LOAD             0x20
> +#define EP93XX_TIMER2_VALUE            0x24
> +#define EP93XX_TIMER2_CONTROL          0x28
> +#define EP93XX_TIMER2_CLEAR            0x2c
> +/* This read-only register contains the low word of the time stamp debug timer
> + * ( Timer4). When this register is read, the high byte of the Timer4 counter is
> + * saved in the Timer4ValueHigh register.
> + */
> +#define EP93XX_TIMER4_VALUE_LOW                0x60
> +#define EP93XX_TIMER4_VALUE_HIGH       0x64
> +#define EP93XX_TIMER4_VALUE_HIGH_ENABLE        BIT(8)
> +#define EP93XX_TIMER3_LOAD             0x80
> +#define EP93XX_TIMER3_VALUE            0x84
> +#define EP93XX_TIMER3_CONTROL          0x88
> +#define EP93XX_TIMER3_CLEAR            0x8c
> +
> +#define EP93XX_TIMER123_RATE           508469
> +#define EP93XX_TIMER4_RATE             983040
> +
> +struct ep93xx_tcu {
> +       void __iomem *base;
> +};
> +
> +static struct ep93xx_tcu *ep93xx_tcu;
> +
> +static u64 ep93xx_clocksource_read(struct clocksource *c)
> +{
> +       struct ep93xx_tcu *tcu = ep93xx_tcu;
> +       u64 ret;
> +
> +       ret = readl(tcu->base + EP93XX_TIMER4_VALUE_LOW);
> +       ret |= ((u64) (readl(tcu->base + EP93XX_TIMER4_VALUE_HIGH) & 0xff) << 32);
> +       return (u64) ret;
> +}
> +
> +static u64 notrace ep93xx_read_sched_clock(void)
> +{
> +       return ep93xx_clocksource_read(NULL);
> +}
> +
> +static int ep93xx_clkevt_set_next_event(unsigned long next,
> +                                       struct clock_event_device *evt)
> +{
> +       struct ep93xx_tcu *tcu = ep93xx_tcu;
> +       /* Default mode: periodic, off, 508 kHz */
> +       u32 tmode = EP93XX_TIMER123_CONTROL_MODE |
> +       EP93XX_TIMER123_CONTROL_CLKSEL;
> +
> +       /* Clear timer */
> +       writel(tmode, tcu->base + EP93XX_TIMER3_CONTROL);
> +
> +       /* Set next event */
> +       writel(next, tcu->base + EP93XX_TIMER3_LOAD);
> +       writel(tmode | EP93XX_TIMER123_CONTROL_ENABLE,
> +              tcu->base + EP93XX_TIMER3_CONTROL);
> +       return 0;
> +}
> +
> +static int ep93xx_clkevt_shutdown(struct clock_event_device *evt)
> +{
> +       struct ep93xx_tcu *tcu = ep93xx_tcu;
> +       /* Disable timer */
> +       writel(0, tcu->base + EP93XX_TIMER3_CONTROL);
> +
> +       return 0;
> +}
> +
> +static struct clock_event_device ep93xx_clockevent = {
> +       .name                   = "timer1",
> +       .features               = CLOCK_EVT_FEAT_ONESHOT,
> +       .set_state_shutdown     = ep93xx_clkevt_shutdown,
> +       .set_state_oneshot      = ep93xx_clkevt_shutdown,
> +       .tick_resume            = ep93xx_clkevt_shutdown,
> +       .set_next_event         = ep93xx_clkevt_set_next_event,
> +       .rating                 = 300,
> +};
> +
> +static irqreturn_t ep93xx_timer_interrupt(int irq, void *dev_id)
> +{
> +       struct ep93xx_tcu *tcu = ep93xx_tcu;
> +       struct clock_event_device *evt = dev_id;
> +
> +       /* Writing any value clears the timer interrupt */
> +       writel(1, tcu->base + EP93XX_TIMER3_CLEAR);
> +
> +       evt->event_handler(evt);
> +
> +       return IRQ_HANDLED;
> +}
> +
> +static int __init ep93xx_timer_of_init(struct device_node *np)
> +{
> +       int irq;
> +       unsigned long flags = IRQF_TIMER | IRQF_IRQPOLL;
> +       struct ep93xx_tcu *tcu;
> +       int ret;
> +
> +       tcu = kzalloc(sizeof(*tcu), GFP_KERNEL);
> +       if (!tcu)
> +               return -ENOMEM;
> +
> +       tcu->base = of_iomap(np, 0);
> +       if (!tcu->base) {
> +               pr_err("Can't remap registers\n");
> +               ret = -ENXIO;
> +               goto out_free;
> +       }
> +
> +       ep93xx_tcu = tcu;
> +
> +       irq = irq_of_parse_and_map(np, 0);
> +       if (irq <= 0) {
> +               pr_err("ERROR: invalid interrupt number\n");
> +               ret = -EINVAL;
> +               goto out_free;
> +       }
> +
> +       /* Enable and register clocksource and sched_clock on timer 4 */
> +       writel(EP93XX_TIMER4_VALUE_HIGH_ENABLE,
> +              tcu->base + EP93XX_TIMER4_VALUE_HIGH);
> +       clocksource_mmio_init(NULL, "timer4",
> +                               EP93XX_TIMER4_RATE, 200, 40,
> +                               ep93xx_clocksource_read);
> +       sched_clock_register(ep93xx_read_sched_clock, 40,
> +                            EP93XX_TIMER4_RATE);
> +
> +       /* Set up clockevent on timer 3 */
> +       if (request_irq(irq, ep93xx_timer_interrupt, flags, "ep93xx timer",
> +               &ep93xx_clockevent))
> +               pr_err("Failed to request irq %d (ep93xx timer)\n", irq);
> +       clockevents_config_and_register(&ep93xx_clockevent,
> +                               EP93XX_TIMER123_RATE,
> +                               1,
> +                               0xffffffffU);
> +
> +       return 0;
> +
> +out_free:
> +       kfree(tcu);
> +       return ret;
> +}
> +
> +TIMER_OF_DECLARE(ep93xx_timer, "cirrus,ep9301-timer", ep93xx_timer_of_init);

--
Alexander Sverdlin.