7 files changed, 442 insertions, 2 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c45513d806ab..a92c5ebf373e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2543,6 +2543,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
         sched_debug     [KNL] Enables verbose scheduler debug messages.
 
+        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
+                        xtime_lock contention on larger systems, and/or RCU lock
+                        contention on all systems with CONFIG_MAXSMP set.
+                        Format: { "0" | "1" }
+                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
+                        1 -- enable.
+                        Note: increases power consumption, thus should only be
+                        enabled if running jitter sensitive (HPC/RT) workloads.
+
         security=       [SECURITY] Choose a security module to enable at boot.
                         If this boot parameter is not specified, only the first
                         security module asking for security registration will be
diff --git a/arch/arm/mach-shmobile/Kconfig b/arch/arm/mach-shmobile/Kconfig
index f31383c32f9c..df33909205e2 100644
--- a/arch/arm/mach-shmobile/Kconfig
+++ b/arch/arm/mach-shmobile/Kconfig
@@ -186,6 +186,12 @@ config SH_TIMER_TMU
         help
           This enables build of the TMU timer driver.
 
+config EM_TIMER_STI
+        bool "STI timer driver"
+        default y
+        help
+          This enables build of the STI timer driver.
+
 endmenu
 
 config SH_CLK_CPG
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 8d81a1d32653..dd3e661a124d 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -6,6 +6,7 @@ obj-$(CONFIG_CS5535_CLOCK_EVENT_SRC)	+= cs5535-clockevt.o
 obj-$(CONFIG_SH_TIMER_CMT)      += sh_cmt.o
 obj-$(CONFIG_SH_TIMER_MTU2)     += sh_mtu2.o
 obj-$(CONFIG_SH_TIMER_TMU)      += sh_tmu.o
+obj-$(CONFIG_EM_TIMER_STI)      += em_sti.o
 obj-$(CONFIG_CLKBLD_I8253)      += i8253.o
 obj-$(CONFIG_CLKSRC_MMIO)       += mmio.o
 obj-$(CONFIG_DW_APB_TIMER)      += dw_apb_timer.o
diff --git a/drivers/clocksource/em_sti.c b/drivers/clocksource/em_sti.c
new file mode 100644
index 000000000000..372051d1bba8
--- /dev/null
+++ b/drivers/clocksource/em_sti.c
@@ -0,0 +1,406 @@
+/*
+ * Emma Mobile Timer Support - STI
+ *
+ *  Copyright (C) 2012 Magnus Damm
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/spinlock.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/io.h>
+#include <linux/clk.h>
+#include <linux/irq.h>
+#include <linux/err.h>
+#include <linux/delay.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+enum { USER_CLOCKSOURCE, USER_CLOCKEVENT, USER_NR };
+
+struct em_sti_priv {
+        void __iomem *base;
+        struct clk *clk;
+        struct platform_device *pdev;
+        unsigned int active[USER_NR];
+        unsigned long rate;
+        raw_spinlock_t lock;
+        struct clock_event_device ced;
+        struct clocksource cs;
+};
+
+#define STI_CONTROL 0x00
+#define STI_COMPA_H 0x10
+#define STI_COMPA_L 0x14
+#define STI_COMPB_H 0x18
+#define STI_COMPB_L 0x1c
+#define STI_COUNT_H 0x20
+#define STI_COUNT_L 0x24
+#define STI_COUNT_RAW_H 0x28
+#define STI_COUNT_RAW_L 0x2c
+#define STI_SET_H 0x30
+#define STI_SET_L 0x34
+#define STI_INTSTATUS 0x40
+#define STI_INTRAWSTATUS 0x44
+#define STI_INTENSET 0x48
+#define STI_INTENCLR 0x4c
+#define STI_INTFFCLR 0x50
+
+static inline unsigned long em_sti_read(struct em_sti_priv *p, int offs)
+{
+        return ioread32(p->base + offs);
+}
+
+static inline void em_sti_write(struct em_sti_priv *p, int offs,
+                                unsigned long value)
+{
+        iowrite32(value, p->base + offs);
+}
+
+static int em_sti_enable(struct em_sti_priv *p)
+{
+        int ret;
+
+        /* enable clock */
+        ret = clk_enable(p->clk);
+        if (ret) {
+                dev_err(&p->pdev->dev, "cannot enable clock\n");
+                return ret;
+        }
+
+        /* configure channel, periodic mode and maximum timeout */
+        p->rate = clk_get_rate(p->clk);
+
+        /* reset the counter */
+        em_sti_write(p, STI_SET_H, 0x40000000);
+        em_sti_write(p, STI_SET_L, 0x00000000);
+
+        /* mask and clear pending interrupts */
+        em_sti_write(p, STI_INTENCLR, 3);
+        em_sti_write(p, STI_INTFFCLR, 3);
+
+        /* enable updates of counter registers */
+        em_sti_write(p, STI_CONTROL, 1);
+
+        return 0;
+}
+
+static void em_sti_disable(struct em_sti_priv *p)
+{
+        /* mask interrupts */
+        em_sti_write(p, STI_INTENCLR, 3);
+
+        /* stop clock */
+        clk_disable(p->clk);
+}
+
+static cycle_t em_sti_count(struct em_sti_priv *p)
+{
+        cycle_t ticks;
+        unsigned long flags;
+
+        /* the STI hardware buffers the 48-bit count, but to
+         * break it out into two 32-bit access the registers
+         * must be accessed in a certain order.
+         * Always read STI_COUNT_H before STI_COUNT_L.
+         */
+        raw_spin_lock_irqsave(&p->lock, flags);
+        ticks = (cycle_t)(em_sti_read(p, STI_COUNT_H) & 0xffff) << 32;
+        ticks |= em_sti_read(p, STI_COUNT_L);
+        raw_spin_unlock_irqrestore(&p->lock, flags);
+
+        return ticks;
+}
+
+static cycle_t em_sti_set_next(struct em_sti_priv *p, cycle_t next)
+{
+        unsigned long flags;
+
+        raw_spin_lock_irqsave(&p->lock, flags);
+
+        /* mask compare A interrupt */
+        em_sti_write(p, STI_INTENCLR, 1);
+
+        /* update compare A value */
+        em_sti_write(p, STI_COMPA_H, next >> 32);
+        em_sti_write(p, STI_COMPA_L, next & 0xffffffff);
+
+        /* clear compare A interrupt source */
+        em_sti_write(p, STI_INTFFCLR, 1);
+
+        /* unmask compare A interrupt */
+        em_sti_write(p, STI_INTENSET, 1);
+
+        raw_spin_unlock_irqrestore(&p->lock, flags);
+
+        return next;
+}
+
+static irqreturn_t em_sti_interrupt(int irq, void *dev_id)
+{
+        struct em_sti_priv *p = dev_id;
+
+        p->ced.event_handler(&p->ced);
+        return IRQ_HANDLED;
+}
+
+static int em_sti_start(struct em_sti_priv *p, unsigned int user)
+{
+        unsigned long flags;
+        int used_before;
+        int ret = 0;
+
+        raw_spin_lock_irqsave(&p->lock, flags);
+        used_before = p->active[USER_CLOCKSOURCE] | p->active[USER_CLOCKEVENT];
+        if (!used_before)
+                ret = em_sti_enable(p);
+
+        if (!ret)
+                p->active[user] = 1;
+        raw_spin_unlock_irqrestore(&p->lock, flags);
+
+        return ret;
+}
+
+static void em_sti_stop(struct em_sti_priv *p, unsigned int user)
+{
+        unsigned long flags;
+        int used_before, used_after;
+
+        raw_spin_lock_irqsave(&p->lock, flags);
+        used_before = p->active[USER_CLOCKSOURCE] | p->active[USER_CLOCKEVENT];
+        p->active[user] = 0;
+        used_after = p->active[USER_CLOCKSOURCE] | p->active[USER_CLOCKEVENT];
+
+        if (used_before && !used_after)
+                em_sti_disable(p);
+        raw_spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static struct em_sti_priv *cs_to_em_sti(struct clocksource *cs)
+{
+        return container_of(cs, struct em_sti_priv, cs);
+}
+
+static cycle_t em_sti_clocksource_read(struct clocksource *cs)
+{
+        return em_sti_count(cs_to_em_sti(cs));
+}
+
+static int em_sti_clocksource_enable(struct clocksource *cs)
+{
+        int ret;
+        struct em_sti_priv *p = cs_to_em_sti(cs);
+
+        ret = em_sti_start(p, USER_CLOCKSOURCE);
+        if (!ret)
+                __clocksource_updatefreq_hz(cs, p->rate);
+        return ret;
+}
+
+static void em_sti_clocksource_disable(struct clocksource *cs)
+{
+        em_sti_stop(cs_to_em_sti(cs), USER_CLOCKSOURCE);
+}
+
+static void em_sti_clocksource_resume(struct clocksource *cs)
+{
+        em_sti_clocksource_enable(cs);
+}
+
+static int em_sti_register_clocksource(struct em_sti_priv *p)
+{
+        struct clocksource *cs = &p->cs;
+
+        memset(cs, 0, sizeof(*cs));
+        cs->name = dev_name(&p->pdev->dev);
+        cs->rating = 200;
+        cs->read = em_sti_clocksource_read;
+        cs->enable = em_sti_clocksource_enable;
+        cs->disable = em_sti_clocksource_disable;
+        cs->suspend = em_sti_clocksource_disable;
+        cs->resume = em_sti_clocksource_resume;
+        cs->mask = CLOCKSOURCE_MASK(48);
+        cs->flags = CLOCK_SOURCE_IS_CONTINUOUS;
+
+        dev_info(&p->pdev->dev, "used as clock source\n");
+
+        /* Register with dummy 1 Hz value, gets updated in ->enable() */
+        clocksource_register_hz(cs, 1);
+        return 0;
+}
+
+static struct em_sti_priv *ced_to_em_sti(struct clock_event_device *ced)
+{
+        return container_of(ced, struct em_sti_priv, ced);
+}
+
+static void em_sti_clock_event_mode(enum clock_event_mode mode,
+                                    struct clock_event_device *ced)
+{
+        struct em_sti_priv *p = ced_to_em_sti(ced);
+
+        /* deal with old setting first */
+        switch (ced->mode) {
+        case CLOCK_EVT_MODE_ONESHOT:
+                em_sti_stop(p, USER_CLOCKEVENT);
+                break;
+        default:
+                break;
+        }
+
+        switch (mode) {
+        case CLOCK_EVT_MODE_ONESHOT:
+                dev_info(&p->pdev->dev, "used for oneshot clock events\n");
+                em_sti_start(p, USER_CLOCKEVENT);
+                clockevents_config(&p->ced, p->rate);
+                break;
+        case CLOCK_EVT_MODE_SHUTDOWN:
+        case CLOCK_EVT_MODE_UNUSED:
+                em_sti_stop(p, USER_CLOCKEVENT);
+                break;
+        default:
+                break;
+        }
+}
+
+static int em_sti_clock_event_next(unsigned long delta,
+                                   struct clock_event_device *ced)
+{
+        struct em_sti_priv *p = ced_to_em_sti(ced);
+        cycle_t next;
+        int safe;
+
+        next = em_sti_set_next(p, em_sti_count(p) + delta);
+        safe = em_sti_count(p) < (next - 1);
+
+        return !safe;
+}
+
+static void em_sti_register_clockevent(struct em_sti_priv *p)
+{
+        struct clock_event_device *ced = &p->ced;
+
+        memset(ced, 0, sizeof(*ced));
+        ced->name = dev_name(&p->pdev->dev);
+        ced->features = CLOCK_EVT_FEAT_ONESHOT;
+        ced->rating = 200;
+        ced->cpumask = cpumask_of(0);
+        ced->set_next_event = em_sti_clock_event_next;
+        ced->set_mode = em_sti_clock_event_mode;
+
+        dev_info(&p->pdev->dev, "used for clock events\n");
+
+        /* Register with dummy 1 Hz value, gets updated in ->set_mode() */
+        clockevents_config_and_register(ced, 1, 2, 0xffffffff);
+}
+
+static int __devinit em_sti_probe(struct platform_device *pdev)
+{
+        struct em_sti_priv *p;
+        struct resource *res;
+        int irq, ret;
+
+        p = kzalloc(sizeof(*p), GFP_KERNEL);
+        if (p == NULL) {
+                dev_err(&pdev->dev, "failed to allocate driver data\n");
+                ret = -ENOMEM;
+                goto err0;
+        }
+
+        p->pdev = pdev;
+        platform_set_drvdata(pdev, p);
+
+        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+        if (!res) {
+                dev_err(&pdev->dev, "failed to get I/O memory\n");
+                ret = -EINVAL;
+                goto err0;
+        }
+
+        irq = platform_get_irq(pdev, 0);
+        if (irq < 0) {
+                dev_err(&pdev->dev, "failed to get irq\n");
+                ret = -EINVAL;
+                goto err0;
+        }
+
+        /* map memory, let base point to the STI instance */
+        p->base = ioremap_nocache(res->start, resource_size(res));
+        if (p->base == NULL) {
+                dev_err(&pdev->dev, "failed to remap I/O memory\n");
+                ret = -ENXIO;
+                goto err0;
+        }
+
+        /* get hold of clock */
+        p->clk = clk_get(&pdev->dev, "sclk");
+        if (IS_ERR(p->clk)) {
+                dev_err(&pdev->dev, "cannot get clock\n");
+                ret = PTR_ERR(p->clk);
+                goto err1;
+        }
+
+        if (request_irq(irq, em_sti_interrupt,
+                        IRQF_TIMER | IRQF_IRQPOLL | IRQF_NOBALANCING,
+                        dev_name(&pdev->dev), p)) {
+                dev_err(&pdev->dev, "failed to request low IRQ\n");
+                ret = -ENOENT;
+                goto err2;
+        }
+
+        raw_spin_lock_init(&p->lock);
+        em_sti_register_clockevent(p);
+        em_sti_register_clocksource(p);
+        return 0;
+
+err2:
+        clk_put(p->clk);
+err1:
+        iounmap(p->base);
+err0:
+        kfree(p);
+        return ret;
+}
+
+static int __devexit em_sti_remove(struct platform_device *pdev)
+{
+        return -EBUSY; /* cannot unregister clockevent and clocksource */
+}
+
+static const struct of_device_id em_sti_dt_ids[] __devinitconst = {
+        { .compatible = "renesas,em-sti", },
+        {},
+};
+MODULE_DEVICE_TABLE(of, em_sti_dt_ids);
+
+static struct platform_driver em_sti_device_driver = {
+        .probe          = em_sti_probe,
+        .remove         = __devexit_p(em_sti_remove),
+        .driver         = {
+                .name   = "em_sti",
+                .of_match_table = em_sti_dt_ids,
+        }
+};
+
+module_platform_driver(em_sti_device_driver);
+
+MODULE_AUTHOR("Magnus Damm");
+MODULE_DESCRIPTION("Renesas Emma Mobile STI Timer Driver");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 81e803e90aa4..acba894374a1 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -132,6 +132,7 @@ extern u64 clockevent_delta2ns(unsigned long latch,
                                struct clock_event_device *evt);
 extern void clockevents_register_device(struct clock_event_device *dev);
 
+extern void clockevents_config(struct clock_event_device *dev, u32 freq);
 extern void clockevents_config_and_register(struct clock_event_device *dev,
                                             u32 freq, unsigned long min_delta,
                                             unsigned long max_delta);
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 9cd928f7a7c6..7e1ce012a851 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -297,8 +297,7 @@ void clockevents_register_device(struct clock_event_device *dev)
 }
 EXPORT_SYMBOL_GPL(clockevents_register_device);
 
-static void clockevents_config(struct clock_event_device *dev,
-                               u32 freq)
+void clockevents_config(struct clock_event_device *dev, u32 freq)
 {
         u64 sec;
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6a3a5b9ff561..efd386667536 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -814,6 +814,16 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
         return HRTIMER_RESTART;
 }
 
+static int sched_skew_tick;
+
+static int __init skew_tick(char *str)
+{
+        get_option(&str, &sched_skew_tick);
+
+        return 0;
+}
+early_param("skew_tick", skew_tick);
+
 /**
  * tick_setup_sched_timer - setup the tick emulation timer
  */
@@ -831,6 +841,14 @@ void tick_setup_sched_timer(void)
         /* Get the next period (per cpu) */
         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
 
+        /* Offset the tick to avert xtime_lock contention. */
+        if (sched_skew_tick) {
+                u64 offset = ktime_to_ns(tick_period) >> 1;
+                do_div(offset, num_possible_cpus());
+                offset *= smp_processor_id();
+                hrtimer_add_expires_ns(&ts->sched_timer, offset);
+        }
+
         for (;;) {
                 hrtimer_forward(&ts->sched_timer, now, tick_period);
                 hrtimer_start_expires(&ts->sched_timer,