sparc: leon: Fix race condition between leon_cycles_offset and timer_interrupt

This makes sure that leon_cycles_offset takes the pending bit into
account and that leon_clear_clock_irq clears the pending bit. Otherwise,
if leon_cycles_offset is executed after the timer has wrapped but before
timer_interrupt has increased timer_cs_internal_counter, time can be
perceived to go backwards.

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/sparc/kernel/leon_kernel.c b/arch/sparc/kernel/leon_kernel.c
index 683c4af..9bbb8f2 100644 (file)
--- a/arch/sparc/kernel/leon_kernel.c
+++ b/arch/sparc/kernel/leon_kernel.c
@@ -37,6 +37,7 @@ unsigned long amba_system_id;
 static DEFINE_SPINLOCK(leon_irq_lock);
 
 static unsigned long leon3_gptimer_idx; /* Timer Index (0..6) within Timer Core */
+static unsigned long leon3_gptimer_ackmask; /* For clearing pending bit */
 unsigned long leon3_gptimer_irq; /* interrupt controller irq number */
 unsigned int sparc_leon_eirq;
 #define LEON_IMASK(cpu) (&leon3_irqctrl_regs->mask[cpu])
@@ -260,11 +261,19 @@ void leon_update_virq_handling(unsigned int virq,
 
 static u32 leon_cycles_offset(void)
 {
-       u32 rld, val, off;
+       u32 rld, val, ctrl, off;
+
        rld = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].rld);
        val = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].val);
-       off = rld - val;
-       return rld - val;
+       ctrl = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].ctrl);
+       if (LEON3_GPTIMER_CTRL_ISPENDING(ctrl)) {
+               val = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].val);
+               off = 2 * rld - val;
+       } else {
+               off = rld - val;
+       }
+
+       return off;
 }
 
 #ifdef CONFIG_SMP
@@ -302,6 +311,7 @@ void __init leon_init_timers(void)
        int ampopts;
        int err;
        u32 config;
+       u32 ctrl;
 
        sparc_config.get_cycles_offset = leon_cycles_offset;
        sparc_config.cs_period = 1000000 / HZ;
@@ -374,6 +384,16 @@ void __init leon_init_timers(void)
        if (!(leon3_gptimer_regs && leon3_irqctrl_regs && leon3_gptimer_irq))
                goto bad;
 
+       ctrl = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].ctrl);
+       LEON3_BYPASS_STORE_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].ctrl,
+                             ctrl | LEON3_GPTIMER_CTRL_PENDING);
+       ctrl = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].ctrl);
+
+       if ((ctrl & LEON3_GPTIMER_CTRL_PENDING) != 0)
+               leon3_gptimer_ackmask = ~LEON3_GPTIMER_CTRL_PENDING;
+       else
+               leon3_gptimer_ackmask = ~0;
+
        LEON3_BYPASS_STORE_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].val, 0);
        LEON3_BYPASS_STORE_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].rld,
                                (((1000000 / HZ) - 1)));
@@ -452,6 +472,11 @@ bad:
 
 static void leon_clear_clock_irq(void)
 {
+       u32 ctrl;
+
+       ctrl = LEON3_BYPASS_LOAD_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].ctrl);
+       LEON3_BYPASS_STORE_PA(&leon3_gptimer_regs->e[leon3_gptimer_idx].ctrl,
+                             ctrl & leon3_gptimer_ackmask);
 }
 
 static void leon_load_profile_irq(int cpu, unsigned int limit)