/*
* 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_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 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_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");
