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

From Dave Johnson <djohnson+linuxmips@sw.starentnetworks.com>:

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 <ralf@linux-mips.org>

diff --git a/arch/mips/sibyte/sb1250/time.c b/arch/mips/sibyte/sb1250/time.c
index adc0b5271a069603de5cafea58a557d6055ff277..1588f6debd90698522d9c278bedbab47d6696808 100644 (file)
--- 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;
+}

diff --git a/arch/mips/sibyte/swarm/setup.c b/arch/mips/sibyte/swarm/setup.c
index b614ca0ddb69fb03b442fff719c25f5af3746881..b661d2425a369bae38caa0b60141449c9f9c6655 100644 (file)
--- a/arch/mips/sibyte/swarm/setup.c
+++ b/arch/mips/sibyte/swarm/setup.c
@@ -70,6 +70,12 @@ const char *get_system_type(void)
        return "SiByte " SIBYTE_BOARD_NAME;
 }
 
+void __init swarm_time_init(void)
+{
+       /* Setup HPT */
+       sb1250_hpt_setup();
+}
+
 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;
 

diff --git a/include/asm-mips/sibyte/sb1250.h b/include/asm-mips/sibyte/sb1250.h
index a474c29cd7017e79393607e33952e9081c41afca..b09e16c93ca020f215a81e7a2b2ec637c1f06345 100644 (file)
--- a/include/asm-mips/sibyte/sb1250.h
+++ b/include/asm-mips/sibyte/sb1250.h
@@ -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);