Commit a904f747 authored by Ralf Baechle's avatar Ralf Baechle

[MIPS] Sibyte: Fix race in sb1250_gettimeoffset().

From Dave Johnson <>:
sb1250_gettimeoffset() simply reads the current cpu 0 timer remaining
value, however once this counter reaches 0 and the interrupt is raised,
it immediately resets and begins to count down again.
If sb1250_gettimeoffset() is called on cpu 1 via do_gettimeofday() after
the timer has reset but prior to cpu 0 processing the interrupt and
taking write_seqlock() in timer_interrupt() it will return a full value
(or close to it) causing time to jump backwards 1ms. Once cpu 0 handles
the interrupt and timer_interrupt() gets far enough along it will jump
forward 1ms.
Fix this problem by implementing mips_hpt_*() on sb1250 using a spare
timer unrelated to the existing periodic interrupt timers. It runs at
1Mhz with a full 23bit counter.  This eliminated the custom
do_gettimeoffset() for sb1250 and allowed use of the generic
fixed_rate_gettimeoffset() using mips_hpt_*() and timerhi/timerlo.
Signed-off-by: default avatarRalf Baechle <>
parent 4308cb16
......@@ -47,23 +47,51 @@
#define IMR_IP3_VAL K_INT_MAP_I1
#define IMR_IP4_VAL K_INT_MAP_I2
#define SB1250_HPT_NUM 3
#define SB1250_HPT_VALUE M_SCD_TIMER_CNT /* max value */
#define SB1250_HPT_SHIFT ((sizeof(unsigned int)*8)-V_SCD_TIMER_WIDTH)
extern int sb1250_steal_irq(int irq);
static unsigned int sb1250_hpt_read(void);
static void sb1250_hpt_init(unsigned int);
static unsigned int hpt_offset;
void __init sb1250_hpt_setup(void)
int cpu = smp_processor_id();
if (!cpu) {
/* Setup hpt using timer #3 but do not enable irq for it */
* we need to fill 32 bits, so just use the upper 23 bits and pretend
* the timer is going 512Mhz instead of 1Mhz
mips_hpt_frequency = V_SCD_TIMER_FREQ << SB1250_HPT_SHIFT;
mips_hpt_init = sb1250_hpt_init;
mips_hpt_read = sb1250_hpt_read;
void sb1250_time_init(void)
int cpu = smp_processor_id();
int irq = K_INT_TIMER_0+cpu;
/* Only have 4 general purpose timers */
if (cpu > 3) {
/* Only have 4 general purpose timers, and we use last one as hpt */
if (cpu > 2) {
if (!cpu) {
/* Use our own gettimeoffset() routine */
do_gettimeoffset = sb1250_gettimeoffset;
sb1250_mask_irq(cpu, irq);
/* Map the timer interrupt to ip[4] of this cpu */
......@@ -103,7 +131,7 @@ void sb1250_timer_interrupt(struct pt_regs *regs)
int cpu = smp_processor_id();
int irq = K_INT_TIMER_0 + cpu;
/* Reset the timer */
/* ACK interrupt */
......@@ -122,15 +150,26 @@ void sb1250_timer_interrupt(struct pt_regs *regs)
* We use our own do_gettimeoffset() instead of the generic one,
* because the generic one does not work for SMP case.
* In addition, since we use general timer 0 for system time,
* we can get accurate intra-jiffy offset without calibration.
* The HPT is free running from SB1250_HPT_VALUE down to 0 then starts over
* again. There's no easy way to set to a specific value so store init value
* in hpt_offset and subtract each time.
* Note: Timer isn't full 32bits so shift it into the upper part making
* it appear to run at a higher frequency.
unsigned long sb1250_gettimeoffset(void)
static unsigned int sb1250_hpt_read(void)
unsigned long count =
unsigned int count;
return 1000000/HZ - count;
count = (SB1250_HPT_VALUE - count) << SB1250_HPT_SHIFT;
return count - hpt_offset;
static void sb1250_hpt_init(unsigned int count)
hpt_offset = count;
......@@ -70,6 +70,12 @@ const char *get_system_type(void)
return "SiByte " SIBYTE_BOARD_NAME;
void __init swarm_time_init(void)
/* Setup HPT */
void __init swarm_timer_setup(struct irqaction *irq)
......@@ -109,6 +115,7 @@ void __init plat_setup(void)
panic_timeout = 5; /* For debug. */
board_time_init = swarm_time_init;
board_timer_setup = swarm_timer_setup;
board_be_handler = swarm_be_handler;
......@@ -45,8 +45,8 @@ extern unsigned int soc_type;
extern unsigned int periph_rev;
extern unsigned int zbbus_mhz;
extern void sb1250_hpt_setup(void);
extern void sb1250_time_init(void);
extern unsigned long sb1250_gettimeoffset(void);
extern void sb1250_mask_irq(int cpu, int irq);
extern void sb1250_unmask_irq(int cpu, int irq);
extern void sb1250_smp_finish(void);
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment