// SPDX-License-Identifier: GPL-2.0-only
/*
 * Clock event driver for the CS5535/CS5536
 *
 * Copyright (C) 2006, Advanced Micro Devices, Inc.
 * Copyright (C) 2007  Andres Salomon <dilinger@debian.org>
 * Copyright (C) 2009  Andres Salomon <dilinger@collabora.co.uk>
 *
 * The MFGPTs are documented in AMD Geode CS5536 Companion Device Data Book.
 */

#include <linux/kernel.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/cs5535.h>
#include <linux/clockchips.h>

#define DRV_NAME "cs5535-clockevt"

static int timer_irq;
module_param_hw_named(irq, timer_irq, int, irq, 0644);
MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT ticks.");

/*
 * We are using the 32.768kHz input clock - it's the only one that has the
 * ranges we find desirable.  The following table lists the suitable
 * divisors and the associated Hz, minimum interval and the maximum interval:
 *
 *  Divisor   Hz      Min Delta (s)  Max Delta (s)
 *   1        32768   .00048828125      2.000
 *   2        16384   .0009765625       4.000
 *   4         8192   .001953125        8.000
 *   8         4096   .00390625        16.000
 *   16        2048   .0078125         32.000
 *   32        1024   .015625          64.000
 *   64         512   .03125          128.000
 *  128         256   .0625           256.000
 *  256         128   .125            512.000
 */

static struct cs5535_mfgpt_timer *cs5535_event_clock;

/* Selected from the table above */

#define MFGPT_DIVISOR 16
#define MFGPT_SCALE  4     /* divisor = 2^(scale) */
#define MFGPT_HZ  (32768 / MFGPT_DIVISOR)
#define MFGPT_PERIODIC (MFGPT_HZ / HZ)

/*
 * The MFGPT timers on the CS5536 provide us with suitable timers to use
 * as clock event sources - not as good as a HPET or APIC, but certainly
 * better than the PIT.  This isn't a general purpose MFGPT driver, but
 * a simplified one designed specifically to act as a clock event source.
 * For full details about the MFGPT, please consult the CS5536 data sheet.
 */

static void disable_timer(struct cs5535_mfgpt_timer *timer)
{
        /* avoid races by clearing CMP1 and CMP2 unconditionally */
        cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
                        (uint16_t) ~MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP1 |
                                MFGPT_SETUP_CMP2);
}

static void start_timer(struct cs5535_mfgpt_timer *timer, uint16_t delta)
{
        cs5535_mfgpt_write(timer, MFGPT_REG_CMP2, delta);
        cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0);

        cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
                        MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
}

static int mfgpt_shutdown(struct clock_event_device *evt)
{
        disable_timer(cs5535_event_clock);
        return 0;
}

static int mfgpt_set_periodic(struct clock_event_device *evt)
{
        disable_timer(cs5535_event_clock);
        start_timer(cs5535_event_clock, MFGPT_PERIODIC);
        return 0;
}

static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
{
        start_timer(cs5535_event_clock, delta);
        return 0;
}

static struct clock_event_device cs5535_clockevent = {
        .name = DRV_NAME,
        .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
        .set_state_shutdown = mfgpt_shutdown,
        .set_state_periodic = mfgpt_set_periodic,
        .set_state_oneshot = mfgpt_shutdown,
        .tick_resume = mfgpt_shutdown,
        .set_next_event = mfgpt_next_event,
        .rating = 250,
        .owner = THIS_MODULE,
};

static irqreturn_t mfgpt_tick(int irq, void *dev_id)
{
        uint16_t val = cs5535_mfgpt_read(cs5535_event_clock, MFGPT_REG_SETUP);

        /* See if the interrupt was for us */
        if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
                return IRQ_NONE;

        /* Turn off the clock (and clear the event) */
        disable_timer(cs5535_event_clock);

        if (clockevent_state_detached(&cs5535_clockevent) ||
            clockevent_state_shutdown(&cs5535_clockevent))
                return IRQ_HANDLED;

        /* Clear the counter */
        cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);

        /* Restart the clock in periodic mode */

        if (clockevent_state_periodic(&cs5535_clockevent))
                cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
                                MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);

        cs5535_clockevent.event_handler(&cs5535_clockevent);
        return IRQ_HANDLED;
}

static int __init cs5535_mfgpt_init(void)
{
        unsigned long flags = IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED;
        struct cs5535_mfgpt_timer *timer;
        int ret;
        uint16_t val;

        timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
        if (!timer) {
                printk(KERN_ERR DRV_NAME ": Could not allocate MFGPT timer\n");
                return -ENODEV;
        }
        cs5535_event_clock = timer;

        /* Set up the IRQ on the MFGPT side */
        if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
                printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
                                timer_irq);
                goto err_timer;
        }

        /* And register it with the kernel */
        ret = request_irq(timer_irq, mfgpt_tick, flags, DRV_NAME, timer);
        if (ret) {
                printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
                goto err_irq;
        }

        /* Set the clock scale and enable the event mode for CMP2 */
        val = MFGPT_SCALE | (3 << 8);

        cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);

        /* Set up the clock event */
        printk(KERN_INFO DRV_NAME
                ": Registering MFGPT timer as a clock event, using IRQ %d\n",
                timer_irq);
        clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ,
                                        0xF, 0xFFFE);

        return 0;

err_irq:
        cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
err_timer:
        cs5535_mfgpt_free_timer(cs5535_event_clock);
        printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
        return -EIO;
}

module_init(cs5535_mfgpt_init);

MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
MODULE_LICENSE("GPL");