diff options
Diffstat (limited to 'arch/ppc/platforms/chrp_time.c')
| -rw-r--r-- | arch/ppc/platforms/chrp_time.c | 64 |
1 files changed, 63 insertions, 1 deletions
diff --git a/arch/ppc/platforms/chrp_time.c b/arch/ppc/platforms/chrp_time.c index 29d074c305f..57753a55b58 100644 --- a/arch/ppc/platforms/chrp_time.c +++ b/arch/ppc/platforms/chrp_time.c @@ -163,13 +163,75 @@ unsigned long chrp_get_rtc_time(void) return mktime(year, mon, day, hour, min, sec); } +/* + * Calibrate the decrementer frequency with the VIA timer 1. + */ +#define VIA_TIMER_FREQ_6 4700000 /* time 1 frequency * 6 */ + +/* VIA registers */ +#define RS 0x200 /* skip between registers */ +#define T1CL (4*RS) /* Timer 1 ctr/latch (low 8 bits) */ +#define T1CH (5*RS) /* Timer 1 counter (high 8 bits) */ +#define T1LL (6*RS) /* Timer 1 latch (low 8 bits) */ +#define T1LH (7*RS) /* Timer 1 latch (high 8 bits) */ +#define ACR (11*RS) /* Auxiliary control register */ +#define IFR (13*RS) /* Interrupt flag register */ + +/* Bits in ACR */ +#define T1MODE 0xc0 /* Timer 1 mode */ +#define T1MODE_CONT 0x40 /* continuous interrupts */ + +/* Bits in IFR and IER */ +#define T1_INT 0x40 /* Timer 1 interrupt */ + +static int __init chrp_via_calibrate_decr(void) +{ + struct device_node *vias; + volatile unsigned char __iomem *via; + int count = VIA_TIMER_FREQ_6 / 100; + unsigned int dstart, dend; + + vias = find_devices("via-cuda"); + if (vias == 0) + vias = find_devices("via"); + if (vias == 0 || vias->n_addrs == 0) + return 0; + via = ioremap(vias->addrs[0].address, vias->addrs[0].size); + + /* set timer 1 for continuous interrupts */ + out_8(&via[ACR], (via[ACR] & ~T1MODE) | T1MODE_CONT); + /* set the counter to a small value */ + out_8(&via[T1CH], 2); + /* set the latch to `count' */ + out_8(&via[T1LL], count); + out_8(&via[T1LH], count >> 8); + /* wait until it hits 0 */ + while ((in_8(&via[IFR]) & T1_INT) == 0) + ; + dstart = get_dec(); + /* clear the interrupt & wait until it hits 0 again */ + in_8(&via[T1CL]); + while ((in_8(&via[IFR]) & T1_INT) == 0) + ; + dend = get_dec(); + + tb_ticks_per_jiffy = (dstart - dend) / ((6 * HZ)/100); + tb_to_us = mulhwu_scale_factor(dstart - dend, 60000); + + printk(KERN_INFO "via_calibrate_decr: ticks per jiffy = %u (%u ticks)\n", + tb_ticks_per_jiffy, dstart - dend); + + iounmap(via); + + return 1; +} void __init chrp_calibrate_decr(void) { struct device_node *cpu; unsigned int freq, *fp; - if (via_calibrate_decr()) + if (chrp_via_calibrate_decr()) return; /* |