[Minios-devel] [UNIKRAFT PATCH 7/7] plat/common: Implement generic_timer_cpu_block

[Wei Chen <wei.chen@xxxxxxx>]

This function will be used when system enter sleep and need wakeup
in a specific time. For ns_to_ticks precision, we limited the max
sleep time to 3600 seconds.

Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
Signed-off-by: Jianyong Wu <jianyong.wu@xxxxxxx>
---
 plat/common/arm/time.c | 78 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 5 deletions(-)

diff --git a/plat/common/arm/time.c b/plat/common/arm/time.c
index ae539a0..46f5f93 100644
--- a/plat/common/arm/time.c
+++ b/plat/common/arm/time.c
@@ -76,6 +76,11 @@ static uint32_t tick_per_ns;
  */
 #define __MAX_CONVERT_SECS     3600UL
 
+/*
+ * Minimum delta to sleep using generic timer.
+ */
+static uint32_t counter_mini_delta;
+
 /* How many nanoseconds per second */
 #define NSEC_PER_SEC ukarch_time_sec_to_nsec(1)
 
@@ -219,6 +224,67 @@ static uint64_t generic_timer_epochoffset(void)
        return 0;
 }
 
+/*
+ * Returns early if any interrupts are serviced, or if the requested delay is
+ * too short. Must be called with interrupts disabled, will enable interrupts
+ * "atomically" during idle loop.
+ *
+ * This function must be called only from the scheduler. It will screw
+ * your system if you do otherwise. And, there is no reason you
+ * actually want to use it anywhere else. THIS IS NOT A YIELD or any
+ * kind of mutex_lock. It will simply halt the cpu, not allowing any
+ * other thread to execute.
+ */
+static void generic_timer_cpu_block(uint64_t until_ns)
+{
+       uint64_t now_ns, delta_ns;
+       uint64_t now_ticks, delta_ticks;
+
+       UK_ASSERT(ukplat_lcpu_irqs_disabled());
+
+       /* Record current ticks */
+       now_ticks = generic_timer_get_ticks();
+       now_ns = ticks_to_ns(now_ticks - boot_ticks);
+
+       /*
+        * Compute delta in counter ticks. Return if it is less than minimum
+        * safe amount of ticks. Essentially this will cause us to spin until
+        * the timeout.
+        */
+       delta_ns = until_ns - now_ns;
+       delta_ticks = ns_to_ticks(delta_ns);
+       if (delta_ticks < counter_mini_delta) {
+               /*
+                * Since we are "spinning", quickly enable interrupts in
+                * the hopes that we might get new work and can do something
+                * else than spin.
+                */
+               ukplat_lcpu_enable_irq();
+               nop();
+               ukplat_lcpu_disable_irq();
+
+               return;
+       }
+
+       /* Calculate the next match ticks for compare counter */
+       generic_timer_update_compare(now_ticks + delta_ticks);
+
+       /* Unmask the IRQ for next match interrupt */
+       generic_timer_unmask_irq();
+
+       /*
+        * Wait for any interrupt. If we got an interrupt then just
+        * return into the scheduler (this func is called _ONLY_ from
+        * a scheduler, see the note above) which will check if there
+        * is work to do and call us again here if not.
+        *
+        * TODO: It would be more efficient for longer sleeps to be
+        * able to distinguish if the interrupt was the timer interrupt
+        * and no other, but this will do for now.
+        */
+       ukplat_lcpu_halt_irq();
+}
+
 static int generic_timer_init(int fdt_timer)
 {
        /* Get counter frequency from DTB or register */
@@ -244,6 +310,12 @@ static int generic_timer_init(int fdt_timer)
        /* We disallow zero ns_per_tick */
        UK_BUGON(!tick_per_ns);
 
+       /*
+        * Set minimal counter delta, programming seems to have an overhead
+        * of 3-4us, but play it safe here.
+        */
+       counter_mini_delta = ns_to_ticks(4000);
+
        return 0;
 }
 
@@ -264,11 +336,7 @@ unsigned long sched_have_pending_events;
 void time_block_until(__snsec until)
 {
        while ((__snsec) ukplat_monotonic_clock() < until) {
-               /*
-                * TODO:
-                * As we haven't support interrupt on Arm, so we just
-                * use busy polling for now.
-                */
+               generic_timer_cpu_block(until);
                if (__uk_test_and_clear_bit(0, &sched_have_pending_events))
                        break;
        }
-- 
2.17.1


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