diff options
Diffstat (limited to 'drivers/clocksource/cs5535-clockevt.c')
| -rw-r--r-- | drivers/clocksource/cs5535-clockevt.c | 196 |
1 files changed, 196 insertions, 0 deletions
diff --git a/drivers/clocksource/cs5535-clockevt.c b/drivers/clocksource/cs5535-clockevt.c new file mode 100644 index 000000000..1de8cac99 --- /dev/null +++ b/drivers/clocksource/cs5535-clockevt.c @@ -0,0 +1,196 @@ +/* + * 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; +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, +}; + +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 struct irqaction mfgptirq = { + .handler = mfgpt_tick, + .flags = IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED, + .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 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 = setup_irq(timer_irq, &mfgptirq); + 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"); |