From a904f7478561464f9fe74929b81fec237b6ff4c3 Mon Sep 17 00:00:00 2001 From: Ralf Baechle Date: Wed, 15 Mar 2006 00:03:29 +0000 Subject: [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: Ralf Baechle --- arch/mips/sibyte/sb1250/time.c | 73 ++++++++++++++++++++++++++++++++---------- 1 file changed, 56 insertions(+), 17 deletions(-) (limited to 'arch/mips/sibyte/sb1250') diff --git a/arch/mips/sibyte/sb1250/time.c b/arch/mips/sibyte/sb1250/time.c index adc0b5271a06..1588f6debd90 100644 --- a/arch/mips/sibyte/sb1250/time.c +++ b/arch/mips/sibyte/sb1250/time.c @@ -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 */ + __raw_writeq(0, IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_CFG))); + __raw_writeq(SB1250_HPT_VALUE, + IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_INIT))); + __raw_writeq(M_SCD_TIMER_ENABLE | M_SCD_TIMER_MODE_CONTINUOUS, + IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_CFG))); + + /* + * 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) { BUG(); } - 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 */ ____raw_writeq(M_SCD_TIMER_ENABLE | M_SCD_TIMER_MODE_CONTINUOUS, IOADDR(A_SCD_TIMER_REGISTER(cpu, R_SCD_TIMER_CFG))); @@ -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 = - __raw_readq(IOADDR(A_SCD_TIMER_REGISTER(0, R_SCD_TIMER_CNT))); + unsigned int count; - return 1000000/HZ - count; - } + count = G_SCD_TIMER_CNT(__raw_readq(IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_CNT)))); + + count = (SB1250_HPT_VALUE - count) << SB1250_HPT_SHIFT; + + return count - hpt_offset; +} + +static void sb1250_hpt_init(unsigned int count) +{ + hpt_offset = count; + return; +} -- cgit v1.2.2