libpayload/x86/apic: Add an apic_delay method and calibrate the timer

The apic_delay method will halt the CPU and wait for a timer interrupt
to fire. I went with usec because nsec is too granular to guarantee.

This method will be called from an arch_ndelay() method when the delay
is large enough to justify a sleep.

BUG=b:109749762
TEST=Tested it on grunt by changing the _delay method to call
apic_delay().

Change-Id: I80363f06bdb22d0907f895885e607fde1c4c468d
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/28242
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

2 files changed, 79 insertions, 0 deletions

diff --git a/payloads/libpayload/arch/x86/apic.c b/payloads/libpayload/arch/x86/apic.c
index d5cf6ae14f..079f456eec 100644
--- a/payloads/libpayload/arch/x86/apic.c
+++ b/payloads/libpayload/arch/x86/apic.c
@@ -61,8 +61,13 @@
 
 #define APIC_LVT_SIZE			0x010
 
+#define APIC_TIMER_VECTOR		0x20
+
 static uint32_t apic_bar;
 static int _apic_initialized;
+// TODO: Build a lookup table to avoid calculating it.
+static uint32_t ticks_per_ms;
+static volatile uint8_t timer_waiting;
 
 enum APIC_CAPABILITY {
 	DISABLED = 0,
@@ -95,6 +100,47 @@ uint8_t apic_id(void)
 	return id;
 }
 
+void apic_delay(unsigned int usec)
+{
+	die_if(!ticks_per_ms, "apic_init_timer was not run.");
+	die_if(timer_waiting, "timer already started.");
+	die_if(!interrupts_enabled(), "Interrupts disabled.");
+
+	/* The order is important so we don't underflow */
+	uint64_t ticks = usec * ticks_per_ms / USECS_PER_MSEC;
+
+	/* Not enough resolution */
+	if (!ticks)
+		return;
+
+	/* Disable interrupts so we don't get a race condition between
+	 * starting the timer and the hlt instruction. */
+	disable_interrupts();
+
+	timer_waiting = 1;
+
+	apic_write32(APIC_TIMER_INIT_COUNT, ticks);
+
+	/* Loop in case another interrupt has fired and resumed execution. */
+	do {
+		asm volatile(
+			"sti\n\t"
+			"hlt\n\t"
+			/* Disable interrupts to prevent a race condition
+			 * between checking timer_waiting and executing the hlt
+			 * instruction again. */
+			"cli\n\t");
+	} while (timer_waiting);
+
+	/* Leave hardware interrupts enabled. */
+	enable_interrupts();
+}
+
+static void timer_interrupt_handler(u8 vector)
+{
+	timer_waiting = 0;
+}
+
 void apic_eoi(void)
 {
 	die_if(!apic_bar, "APIC is not initialized");
@@ -150,6 +196,33 @@ static void apic_set_task_priority(uint8_t priority)
 	apic_write32(APIC_TASK_PRIORITY, priority);
 }
 
+static void apic_init_timer(void)
+{
+	die_if(!apic_bar, "APIC is not initialized");
+
+	apic_write32(APIC_LVT_TIMER, APIC_MASKED_BIT);
+
+	/* Divide the clock by 1. */
+	apic_write32(APIC_TIMER_DIV_CFG, 0xB);
+
+	/* Calibrate the APIC timer */
+	if (!ticks_per_ms) {
+		/* Set APIC init counter to MAX and count for 1 ms */
+		apic_write32(APIC_TIMER_INIT_COUNT, UINT32_MAX);
+
+		mdelay(1);
+
+		ticks_per_ms =
+			UINT32_MAX - apic_read32(APIC_TIMER_CUR_COUNT);
+	}
+
+	/* Clear the count so we don't get any stale interrupts */
+	apic_write32(APIC_TIMER_INIT_COUNT, 0);
+
+	/* Unmask the timer and set the vector. */
+	apic_write32(APIC_LVT_TIMER, APIC_TIMER_VECTOR);
+}
+
 static void apic_sw_enable(void)
 {
 	uint32_t reg = apic_read32(APIC_SPURIOUS);
@@ -183,6 +256,10 @@ void apic_init(void)
 
 	apic_sw_enable();
 
+	apic_init_timer();
+
+	set_interrupt_handler(APIC_TIMER_VECTOR, &timer_interrupt_handler);
+
 	_apic_initialized = 1;
 
 	printf("APIC Configured\n");
diff --git a/payloads/libpayload/include/x86/arch/apic.h b/payloads/libpayload/include/x86/arch/apic.h
index fdd447361a..ef962f44d8 100644
--- a/payloads/libpayload/include/x86/arch/apic.h
+++ b/payloads/libpayload/include/x86/arch/apic.h
@@ -40,4 +40,6 @@ uint8_t apic_id(void);
 /** Signal the end of the interrupt handler. */
 void apic_eoi(void);
 
+void apic_delay(unsigned int usec);
+
 #endif /* __ARCH_X86_INCLUDES_ARCH_APIC_H__ */