cs5535: add a generic clock event MFGPT driver

This is based on the old code in arch/x86/kernel/mfgpt_32.c, but is
modular and not Geode-specific.  There's no reason why the clock event
device needs to be registered so early at boot; the clockevent code is
perfectly capable of dynamic switching.

[akpm@linux-foundation.org: add linux/irq.h include]
Signed-off-by: Andres Salomon <dilinger@collabora.co.uk>
Cc: Jordan Crouse <jordan@cosmicpenguin.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Chris Ball <cjb@laptop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 207 insertions, 0 deletions

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
new file mode 100644
index 000000000000..08f726c5fee5
--- /dev/null
+++ b/drivers/clocksource/Kconfig
@@ -0,0 +1,9 @@
+config CS5535_CLOCK_EVENT_SRC
+        tristate "CS5535/CS5536 high-res timer (MFGPT) events"
+        depends on GENERIC_TIME && GENERIC_CLOCKEVENTS && CS5535_MFGPT
+        help
+          This driver provides a clock event source based on the MFGPT
+          timer(s) in the CS5535 and CS5536 companion chips.
+          MFGPTs have a better resolution and max interval than the
+          generic PIT, and are suitable for use as high-res timers.
+
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index eef216f7f61d..be61ece6330b 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -2,6 +2,7 @@ obj-$(CONFIG_ATMEL_TCB_CLKSRC)	+= tcb_clksrc.o
 obj-$(CONFIG_X86_CYCLONE_TIMER) += cyclone.o
 obj-$(CONFIG_X86_PM_TIMER)      += acpi_pm.o
 obj-$(CONFIG_SCx200HR_TIMER)    += scx200_hrt.o
+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
diff --git a/drivers/clocksource/cs5535-clockevt.c b/drivers/clocksource/cs5535-clockevt.c
new file mode 100644
index 000000000000..27d20fac19d1
--- /dev/null
+++ b/drivers/clocksource/cs5535-clockevt.c
@@ -0,0 +1,197 @@
+/*
+ * 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>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * 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 = CONFIG_CS5535_MFGPT_DEFAULT_IRQ;
+module_param_named(irq, timer_irq, int, 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 unsigned int cs5535_tick_mode = CLOCK_EVT_MODE_SHUTDOWN;
+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 MFPGT 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 void mfgpt_set_mode(enum clock_event_mode mode,
+                struct clock_event_device *evt)
+{
+        disable_timer(cs5535_event_clock);
+
+        if (mode == CLOCK_EVT_MODE_PERIODIC)
+                start_timer(cs5535_event_clock, MFGPT_PERIODIC);
+
+        cs5535_tick_mode = mode;
+}
+
+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_mode = mfgpt_set_mode,
+        .set_next_event = mfgpt_next_event,
+        .rating = 250,
+        .cpumask = cpu_all_mask,
+        .shift = 32
+};
+
+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 (cs5535_tick_mode == CLOCK_EVT_MODE_SHUTDOWN)
+                return IRQ_HANDLED;
+
+        /* Clear the counter */
+        cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
+
+        /* Restart the clock in periodic mode */
+
+        if (cs5535_tick_mode == CLOCK_EVT_MODE_PERIODIC)
+                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 struct irqaction mfgptirq  = {
+        .handler = mfgpt_tick,
+        .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER,
+        .name = DRV_NAME,
+};
+
+static int __init cs5535_mfgpt_init(void)
+{
+        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 MFPGT 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);
+                return -EIO;
+        }
+
+        /* And register it with the kernel */
+        ret = setup_irq(timer_irq, &mfgptirq);
+        if (ret) {
+                printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
+                goto err;
+        }
+
+        /* 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 */
+        cs5535_clockevent.mult = div_sc(MFGPT_HZ, NSEC_PER_SEC,
+                        cs5535_clockevent.shift);
+        cs5535_clockevent.min_delta_ns = clockevent_delta2ns(0xF,
+                        &cs5535_clockevent);
+        cs5535_clockevent.max_delta_ns = clockevent_delta2ns(0xFFFE,
+                        &cs5535_clockevent);
+
+        printk(KERN_INFO DRV_NAME
+                ": Registering MFGPT timer as a clock event, using IRQ %d\n",
+                timer_irq);
+        clockevents_register_device(&cs5535_clockevent);
+
+        return 0;
+
+err:
+        cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
+        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@collabora.co.uk>");
+MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
+MODULE_LICENSE("GPL");