High Precision Event Timer Driver for Linux
-The High Precision Event Timer (HPET) hardware is the future replacement
-for the 8254 and Real Time Clock (RTC) periodic timer functionality.
-Each HPET can have up to 32 timers. It is possible to configure the
-first two timers as legacy replacements for 8254 and RTC periodic timers.
-A specification done by Intel and Microsoft can be found at
-<http://www.intel.com/technology/architecture/hpetspec.htm>.
+The High Precision Event Timer (HPET) hardware follows a specification
+by Intel and Microsoft which can be found at
+
+ http://www.intel.com/technology/architecture/hpetspec.htm
+
+Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision")
+and up to 32 comparators. Normally three or more comparators are provided,
+each of which can generate oneshot interupts and at least one of which has
+additional hardware to support periodic interrupts. The comparators are
+also called "timers", which can be misleading since usually timers are
+independent of each other ... these share a counter, complicating resets.
+
+HPET devices can support two interrupt routing modes. In one mode, the
+comparators are additional interrupt sources with no particular system
+role. Many x86 BIOS writers don't route HPET interrupts at all, which
+prevents use of that mode. They support the other "legacy replacement"
+mode where the first two comparators block interrupts from 8254 timers
+and from the RTC.
The driver supports detection of HPET driver allocation and initialization
of the HPET before the driver module_init routine is called. This enables
platform code which uses timer 0 or 1 as the main timer to intercept HPET
initialization. An example of this initialization can be found in
-arch/i386/kernel/time_hpet.c.
+arch/x86/kernel/hpet.c.
-The driver provides two APIs which are very similar to the API found in
-the rtc.c driver. There is a user space API and a kernel space API.
-An example user space program is provided below.
+The driver provides a userspace API which resembles the API found in the
+RTC driver framework. An example user space program is provided below.
#include <stdio.h>
#include <stdlib.h>
return;
}
-
-The kernel API has three interfaces exported from the driver:
-
- hpet_register(struct hpet_task *tp, int periodic)
- hpet_unregister(struct hpet_task *tp)
- hpet_control(struct hpet_task *tp, unsigned int cmd, unsigned long arg)
-
-The kernel module using this interface fills in the ht_func and ht_data
-members of the hpet_task structure before calling hpet_register.
-hpet_control simply vectors to the hpet_ioctl routine and has the same
-commands and respective arguments as the user API. hpet_unregister
-is used to terminate usage of the HPET timer reserved by hpet_register.
#define HPET_RANGE_SIZE 1024 /* from HPET spec */
+
+/* WARNING -- don't get confused. These macros are never used
+ * to write the (single) counter, and rarely to read it.
+ * They're badly named; to fix, someday.
+ */
#if BITS_PER_LONG == 64
#define write_counter(V, MC) writeq(V, MC)
#define read_counter(MC) readq(MC)
.rating = 250,
.read = read_hpet,
.mask = CLOCKSOURCE_MASK(64),
- .mult = 0, /*to be caluclated*/
+ .mult = 0, /* to be calculated */
.shift = 10,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
/* A lock for concurrent access by app and isr hpet activity. */
static DEFINE_SPINLOCK(hpet_lock);
-/* A lock for concurrent intermodule access to hpet and isr hpet activity. */
-static DEFINE_SPINLOCK(hpet_task_lock);
#define HPET_DEV_NAME (7)
unsigned long hd_irqdata;
wait_queue_head_t hd_waitqueue;
struct fasync_struct *hd_async_queue;
- struct hpet_task *hd_task;
unsigned int hd_flags;
unsigned int hd_irq;
unsigned int hd_hdwirq;
writel(isr, &devp->hd_hpet->hpet_isr);
spin_unlock(&hpet_lock);
- spin_lock(&hpet_task_lock);
- if (devp->hd_task)
- devp->hd_task->ht_func(devp->hd_task->ht_data);
- spin_unlock(&hpet_task_lock);
-
wake_up_interruptible(&devp->hd_waitqueue);
kill_fasync(&devp->hd_async_queue, SIGIO, POLL_IN);
for (devp = NULL, hpetp = hpets; hpetp && !devp; hpetp = hpetp->hp_next)
for (i = 0; i < hpetp->hp_ntimer; i++)
- if (hpetp->hp_dev[i].hd_flags & HPET_OPEN
- || hpetp->hp_dev[i].hd_task)
+ if (hpetp->hp_dev[i].hd_flags & HPET_OPEN)
continue;
else {
devp = &hpetp->hp_dev[i];
devp->hd_irq = irq;
t = devp->hd_ireqfreq;
v = readq(&timer->hpet_config);
- g = v | Tn_INT_ENB_CNF_MASK;
+
+ /* 64-bit comparators are not yet supported through the ioctls,
+ * so force this into 32-bit mode if it supports both modes
+ */
+ g = v | Tn_32MODE_CNF_MASK | Tn_INT_ENB_CNF_MASK;
if (devp->hd_flags & HPET_PERIODIC) {
write_counter(t, &timer->hpet_compare);
v |= Tn_VAL_SET_CNF_MASK;
writeq(v, &timer->hpet_config);
local_irq_save(flags);
+
+ /* NOTE: what we modify here is a hidden accumulator
+ * register supported by periodic-capable comparators.
+ * We never want to modify the (single) counter; that
+ * would affect all the comparators.
+ */
m = read_counter(&hpet->hpet_mc);
write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
} else {
return 0;
}
-static inline int hpet_tpcheck(struct hpet_task *tp)
-{
- struct hpet_dev *devp;
- struct hpets *hpetp;
-
- devp = tp->ht_opaque;
-
- if (!devp)
- return -ENXIO;
-
- for (hpetp = hpets; hpetp; hpetp = hpetp->hp_next)
- if (devp >= hpetp->hp_dev
- && devp < (hpetp->hp_dev + hpetp->hp_ntimer)
- && devp->hd_hpet == hpetp->hp_hpet)
- return 0;
-
- return -ENXIO;
-}
-
-#if 0
-int hpet_unregister(struct hpet_task *tp)
-{
- struct hpet_dev *devp;
- struct hpet_timer __iomem *timer;
- int err;
-
- if ((err = hpet_tpcheck(tp)))
- return err;
-
- spin_lock_irq(&hpet_task_lock);
- spin_lock(&hpet_lock);
-
- devp = tp->ht_opaque;
- if (devp->hd_task != tp) {
- spin_unlock(&hpet_lock);
- spin_unlock_irq(&hpet_task_lock);
- return -ENXIO;
- }
-
- timer = devp->hd_timer;
- writeq((readq(&timer->hpet_config) & ~Tn_INT_ENB_CNF_MASK),
- &timer->hpet_config);
- devp->hd_flags &= ~(HPET_IE | HPET_PERIODIC);
- devp->hd_task = NULL;
- spin_unlock(&hpet_lock);
- spin_unlock_irq(&hpet_task_lock);
-
- return 0;
-}
-#endif /* 0 */
-
static ctl_table hpet_table[] = {
{
.ctl_name = CTL_UNNUMBERED,
printk("%s %d", i > 0 ? "," : "", hdp->hd_irq[i]);
printk("\n");
- printk(KERN_INFO "hpet%u: %u %d-bit timers, %Lu Hz\n",
- hpetp->hp_which, hpetp->hp_ntimer,
- cap & HPET_COUNTER_SIZE_MASK ? 64 : 32, hpetp->hp_tick_freq);
+ printk(KERN_INFO
+ "hpet%u: %u comparators, %d-bit %u.%06u MHz counter\n",
+ hpetp->hp_which, hpetp->hp_ntimer,
+ cap & HPET_COUNTER_SIZE_MASK ? 64 : 32,
+ (unsigned) (hpetp->hp_tick_freq / 1000000),
+ (unsigned) (hpetp->hp_tick_freq % 1000000));
mcfg = readq(&hpet->hpet_config);
if ((mcfg & HPET_ENABLE_CNF_MASK) == 0) {
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