hpet.c

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#include <core/system.h>
#include <core/arch.h>
#include <cpu/sdt.h>
#include <platform/misc.h>
 
#define HPET_CAP        0x000   /* its high half is the period, in fs */
#define HPET_CNF        0x010
#define HPET_CNT        0x0F0
 
#define CNF_ENABLE      0x1
#define CNF_LEGACY      0x2
 
#define PERIOD_MAX_FS   100000000ULL    /* 100 ns, the most the specification allows */
 
static volatile uint32_t *regs;
static uint64_t period_fs;

static inline uint32_t reg32(unsigned off)
{
    return regs[off / 4];
}

static inline void reg32_write(unsigned off, uint32_t val)
{
    regs[off / 4] = val;
}

uint64_t x86_hpet_read(void)
{
    uint32_t hi, lo;
 
    do {
        hi = reg32(HPET_CNT + 4);
        lo = reg32(HPET_CNT);
    } while (hi != reg32(HPET_CNT + 4));
 
    return (uint64_t) hi << 32 | lo;
}

uint32_t x86_hpet_read32(void)
{
    return reg32(HPET_CNT);
}

uint64_t x86_hpet_period_fs(void)
{
    return period_fs;
}

int x86_hpet_init(void)
{
    struct acpi_hpet *t = x86_acpi_table ? x86_acpi_table("HPET") : NULL;
 
    if (!t || t->header.length < sizeof(*t) || t->address.space != 0 || !t->address.address)
        return -ENODEV;
 
    regs = arch_mmio_map(t->address.address, 1024);
 
    if (!regs)
        return -ENOMEM;
 
    period_fs = reg32(HPET_CAP + 4);
 
    if (!period_fs || period_fs > PERIOD_MAX_FS) {
        printk("hpet: bad period %ld fs\n", period_fs);
        return -ENODEV;
    }
 
    /* start counting from 0, leaving the PIT as it is */
    reg32_write(HPET_CNF, reg32(HPET_CNF) & ~(CNF_ENABLE | CNF_LEGACY));
    reg32_write(HPET_CNT, 0);
    reg32_write(HPET_CNT + 4, 0);
    reg32_write(HPET_CNF, (reg32(HPET_CNF) & ~CNF_LEGACY) | CNF_ENABLE);
 
    printk("hpet: at %p, %ld fs a count\n", (void *) (uintptr_t) t->address.address, period_fs);
    return 0;
}