tcb_clksrc.c

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#include <linux/init.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/irq.h>

#include <linux/clk.h>
#include <linux/err.h>
#include <linux/ioport.h>
#include <linux/io.h>
#include <linux/platform_device.h>
#include <linux/atmel_tc.h>


/*
 * We're configured to use a specific TC block, one that's not hooked
 * up to external hardware, to provide a time solution:
 *
 *   - Two channels combine to create a free-running 32 bit counter
 *     with a base rate of 5+ MHz, packaged as a clocksource (with
 *     resolution better than 200 nsec).
 *   - Some chips support 32 bit counter. A single channel is used for
 *     this 32 bit free-running counter. the second channel is not used.
 *
 *   - The third channel may be used to provide a 16-bit clockevent
 *     source, used in either periodic or oneshot mode.  This runs
 *     at 32 KiHZ, and can handle delays of up to two seconds.
 *
 * A boot clocksource and clockevent source are also currently needed,
 * unless the relevant platforms (ARM/AT91, AVR32/AT32) are changed so
 * this code can be used when init_timers() is called, well before most
 * devices are set up.  (Some low end AT91 parts, which can run uClinux,
 * have only the timers in one TC block... they currently don't support
 * the tclib code, because of that initialization issue.)
 *
 * REVISIT behavior during system suspend states... we should disable
 * all clocks and save the power.  Easily done for clockevent devices,
 * but clocksources won't necessarily get the needed notifications.
 * For deeper system sleep states, this will be mandatory...
 */

static void __iomem *tcaddr;

static cycle_t tc_get_cycles(struct clocksource *cs)
{
    unsigned long   flags;
    u32     lower, upper;

    raw_local_irq_save(flags);
    do {
        upper = __raw_readl(tcaddr + ATMEL_TC_REG(1, CV));
        lower = __raw_readl(tcaddr + ATMEL_TC_REG(0, CV));
    } while (upper != __raw_readl(tcaddr + ATMEL_TC_REG(1, CV)));

    raw_local_irq_restore(flags);
    return (upper << 16) | lower;
}

static cycle_t tc_get_cycles32(struct clocksource *cs)
{
    return __raw_readl(tcaddr + ATMEL_TC_REG(0, CV));
}

static struct clocksource clksrc = {
    .name           = "tcb_clksrc",
    .rating         = 200,
    .read           = tc_get_cycles,
    .mask           = CLOCKSOURCE_MASK(32),
    .flags      = CLOCK_SOURCE_IS_CONTINUOUS,
};

#ifdef CONFIG_GENERIC_CLOCKEVENTS

struct tc_clkevt_device {
    struct clock_event_device   clkevt;
    struct clk          *clk;
    void __iomem            *regs;
};

static struct tc_clkevt_device *to_tc_clkevt(struct clock_event_device *clkevt)
{
    return container_of(clkevt, struct tc_clkevt_device, clkevt);
}

/* For now, we always use the 32K clock ... this optimizes for NO_HZ,
 * because using one of the divided clocks would usually mean the
 * tick rate can never be less than several dozen Hz (vs 0.5 Hz).
 *
 * A divided clock could be good for high resolution timers, since
 * 30.5 usec resolution can seem "low".
 */
static u32 timer_clock;

static void tc_mode(enum clock_event_mode m, struct clock_event_device *d)
{
    struct tc_clkevt_device *tcd = to_tc_clkevt(d);
    void __iomem        *regs = tcd->regs;

    if (tcd->clkevt.mode == CLOCK_EVT_MODE_PERIODIC
            || tcd->clkevt.mode == CLOCK_EVT_MODE_ONESHOT) {
        __raw_writel(0xff, regs + ATMEL_TC_REG(2, IDR));
        __raw_writel(ATMEL_TC_CLKDIS, regs + ATMEL_TC_REG(2, CCR));
        clk_disable(tcd->clk);
    }

    switch (m) {

    /* By not making the gentime core emulate periodic mode on top
     * of oneshot, we get lower overhead and improved accuracy.
     */
    case CLOCK_EVT_MODE_PERIODIC:
        clk_enable(tcd->clk);

        /* slow clock, count up to RC, then irq and restart */
        __raw_writel(timer_clock
                | ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO,
                regs + ATMEL_TC_REG(2, CMR));
        __raw_writel((32768 + HZ/2) / HZ, tcaddr + ATMEL_TC_REG(2, RC));

        /* Enable clock and interrupts on RC compare */
        __raw_writel(ATMEL_TC_CPCS, regs + ATMEL_TC_REG(2, IER));

        /* go go gadget! */
        __raw_writel(ATMEL_TC_CLKEN | ATMEL_TC_SWTRG,
                regs + ATMEL_TC_REG(2, CCR));
        break;

    case CLOCK_EVT_MODE_ONESHOT:
        clk_enable(tcd->clk);

        /* slow clock, count up to RC, then irq and stop */
        __raw_writel(timer_clock | ATMEL_TC_CPCSTOP
                | ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO,
                regs + ATMEL_TC_REG(2, CMR));
        __raw_writel(ATMEL_TC_CPCS, regs + ATMEL_TC_REG(2, IER));

        /* set_next_event() configures and starts the timer */
        break;

    default:
        break;
    }
}

static int tc_next_event(unsigned long delta, struct clock_event_device *d)
{
    __raw_writel(delta, tcaddr + ATMEL_TC_REG(2, RC));

    /* go go gadget! */
    __raw_writel(ATMEL_TC_CLKEN | ATMEL_TC_SWTRG,
            tcaddr + ATMEL_TC_REG(2, CCR));
    return 0;
}

static struct tc_clkevt_device clkevt = {
    .clkevt = {
        .name       = "tc_clkevt",
        .features   = CLOCK_EVT_FEAT_PERIODIC
                    | CLOCK_EVT_FEAT_ONESHOT,
        .shift      = 32,
        /* Should be lower than at91rm9200's system timer */
        .rating     = 125,
        .set_next_event = tc_next_event,
        .set_mode   = tc_mode,
    },
};

static irqreturn_t ch2_irq(int irq, void *handle)
{
    struct tc_clkevt_device *dev = handle;
    unsigned int        sr;

    sr = __raw_readl(dev->regs + ATMEL_TC_REG(2, SR));
    if (sr & ATMEL_TC_CPCS) {
        dev->clkevt.event_handler(&dev->clkevt);
        return IRQ_HANDLED;
    }

    return IRQ_NONE;
}

static struct irqaction tc_irqaction = {
    .name       = "tc_clkevt",
    .flags      = IRQF_TIMER | IRQF_DISABLED,
    .handler    = ch2_irq,
};

static void __init setup_clkevents(struct atmel_tc *tc, int clk32k_divisor_idx)
{
    struct clk *t2_clk = tc->clk[2];
    int irq = tc->irq[2];

    clkevt.regs = tc->regs;
    clkevt.clk = t2_clk;
    tc_irqaction.dev_id = &clkevt;

    timer_clock = clk32k_divisor_idx;

    clkevt.clkevt.mult = div_sc(32768, NSEC_PER_SEC, clkevt.clkevt.shift);
    clkevt.clkevt.max_delta_ns
        = clockevent_delta2ns(0xffff, &clkevt.clkevt);
    clkevt.clkevt.min_delta_ns = clockevent_delta2ns(1, &clkevt.clkevt) + 1;
    clkevt.clkevt.cpumask = cpumask_of(0);

    clockevents_register_device(&clkevt.clkevt);

    setup_irq(irq, &tc_irqaction);
}

#else /* !CONFIG_GENERIC_CLOCKEVENTS */

static void __init setup_clkevents(struct atmel_tc *tc, int clk32k_divisor_idx)
{
    /* NOTHING */
}

#endif

static void __init tcb_setup_dual_chan(struct atmel_tc *tc, int mck_divisor_idx)
{
    /* channel 0:  waveform mode, input mclk/8, clock TIOA0 on overflow */
    __raw_writel(mck_divisor_idx            /* likely divide-by-8 */
            | ATMEL_TC_WAVE
            | ATMEL_TC_WAVESEL_UP       /* free-run */
            | ATMEL_TC_ACPA_SET     /* TIOA0 rises at 0 */
            | ATMEL_TC_ACPC_CLEAR,      /* (duty cycle 50%) */
            tcaddr + ATMEL_TC_REG(0, CMR));
    __raw_writel(0x0000, tcaddr + ATMEL_TC_REG(0, RA));
    __raw_writel(0x8000, tcaddr + ATMEL_TC_REG(0, RC));
    __raw_writel(0xff, tcaddr + ATMEL_TC_REG(0, IDR));  /* no irqs */
    __raw_writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(0, CCR));

    /* channel 1:  waveform mode, input TIOA0 */
    __raw_writel(ATMEL_TC_XC1           /* input: TIOA0 */
            | ATMEL_TC_WAVE
            | ATMEL_TC_WAVESEL_UP,      /* free-run */
            tcaddr + ATMEL_TC_REG(1, CMR));
    __raw_writel(0xff, tcaddr + ATMEL_TC_REG(1, IDR));  /* no irqs */
    __raw_writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(1, CCR));

    /* chain channel 0 to channel 1*/
    __raw_writel(ATMEL_TC_TC1XC1S_TIOA0, tcaddr + ATMEL_TC_BMR);
    /* then reset all the timers */
    __raw_writel(ATMEL_TC_SYNC, tcaddr + ATMEL_TC_BCR);
}

static void __init tcb_setup_single_chan(struct atmel_tc *tc, int mck_divisor_idx)
{
    /* channel 0:  waveform mode, input mclk/8 */
    __raw_writel(mck_divisor_idx            /* likely divide-by-8 */
            | ATMEL_TC_WAVE
            | ATMEL_TC_WAVESEL_UP,      /* free-run */
            tcaddr + ATMEL_TC_REG(0, CMR));
    __raw_writel(0xff, tcaddr + ATMEL_TC_REG(0, IDR));  /* no irqs */
    __raw_writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(0, CCR));

    /* then reset all the timers */
    __raw_writel(ATMEL_TC_SYNC, tcaddr + ATMEL_TC_BCR);
}

static int __init tcb_clksrc_init(void)
{
    static char bootinfo[] __initdata
        = KERN_DEBUG "%s: tc%d at %d.%03d MHz\n";

    struct platform_device *pdev;
    struct atmel_tc *tc;
    struct clk *t0_clk;
    u32 rate, divided_rate = 0;
    int best_divisor_idx = -1;
    int clk32k_divisor_idx = -1;
    int i;

    tc = atmel_tc_alloc(CONFIG_ATMEL_TCB_CLKSRC_BLOCK, clksrc.name);
    if (!tc) {
        pr_debug("can't alloc TC for clocksource\n");
        return -ENODEV;
    }
    tcaddr = tc->regs;
    pdev = tc->pdev;

    t0_clk = tc->clk[0];
    clk_enable(t0_clk);

    /* How fast will we be counting?  Pick something over 5 MHz.  */
    rate = (u32) clk_get_rate(t0_clk);
    for (i = 0; i < 5; i++) {
        unsigned divisor = atmel_tc_divisors[i];
        unsigned tmp;

        /* remember 32 KiHz clock for later */
        if (!divisor) {
            clk32k_divisor_idx = i;
            continue;
        }

        tmp = rate / divisor;
        pr_debug("TC: %u / %-3u [%d] --> %u\n", rate, divisor, i, tmp);
        if (best_divisor_idx > 0) {
            if (tmp < 5 * 1000 * 1000)
                continue;
        }
        divided_rate = tmp;
        best_divisor_idx = i;
    }


    printk(bootinfo, clksrc.name, CONFIG_ATMEL_TCB_CLKSRC_BLOCK,
            divided_rate / 1000000,
            ((divided_rate + 500000) % 1000000) / 1000);

    if (tc->tcb_config && tc->tcb_config->counter_width == 32) {
        /* use apropriate function to read 32 bit counter */
        clksrc.read = tc_get_cycles32;
        /* setup ony channel 0 */
        tcb_setup_single_chan(tc, best_divisor_idx);
    } else {
        /* tclib will give us three clocks no matter what the
         * underlying platform supports.
         */
        clk_enable(tc->clk[1]);
        /* setup both channel 0 & 1 */
        tcb_setup_dual_chan(tc, best_divisor_idx);
    }

    /* and away we go! */
    clocksource_register_hz(&clksrc, divided_rate);

    /* channel 2:  periodic and oneshot timer support */
    setup_clkevents(tc, clk32k_divisor_idx);

    return 0;
}
arch_initcall(tcb_clksrc_init);