lib: utils/timer: Simplify MTIMER synchronization

We simplify MTIMER synchronization as follows:

1) Detect MTIMER devices with unique (or non-shared) MTIME
   register at boot-time
2) Select first MTIMER device with no associated HART as our
   reference MTIMER device
3) Only synchronize MTIMER devices with unique (or non-shared)
   MTIME register using reference MTIMER device
4) Directly update the MTIME register at time of synchronization
   because MTIME is a read/write register.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

include/sbi_utils/timer/aclint_mtimer.h

@@ -31,14 +31,19 @@ struct aclint_mtimer_data {
 	u32 first_hartid;
 	u32 hart_count;
 	bool has_64bit_mmio;
+	bool has_shared_mtime;
 	/* Private details (initialized and used by ACLINT MTIMER library) */
 	struct aclint_mtimer_data *time_delta_reference;
 	unsigned long time_delta_computed;
-	u64 time_delta;
 	u64 (*time_rd)(volatile u64 *addr);
 	void (*time_wr)(bool timecmp, u64 value, volatile u64 *addr);
 };
 
+void aclint_mtimer_sync(struct aclint_mtimer_data *mt);
+
+void aclint_mtimer_set_reference(struct aclint_mtimer_data *mt,
+				 struct aclint_mtimer_data *ref);
+
 int aclint_mtimer_warm_init(void);
 
 int aclint_mtimer_cold_init(struct aclint_mtimer_data *mt,

lib/utils/timer/aclint_mtimer.c

@@ -57,7 +57,7 @@ static u64 mtimer_value(void)
 	u64 *time_val = (void *)mt->mtime_addr;
 
 	/* Read MTIMER Time Value */
-	return mt->time_rd(time_val) + mt->time_delta;
+	return mt->time_rd(time_val);
 }
 
 static void mtimer_event_stop(void)
@@ -77,7 +77,7 @@ static void mtimer_event_start(u64 next_event)
 	u64 *time_cmp = (void *)mt->mtimecmp_addr;
 
 	/* Program MTIMER Time Compare */
-	mt->time_wr(true, next_event - mt->time_delta,
+	mt->time_wr(true, next_event,
 		    &time_cmp[target_hart - mt->first_hartid]);
 }
 
@@ -88,36 +88,51 @@ static struct sbi_timer_device mtimer = {
 	.timer_event_stop = mtimer_event_stop
 };
 
+void aclint_mtimer_sync(struct aclint_mtimer_data *mt)
+{
+	u64 v1, v2, mv, delta;
+	u64 *mt_time_val, *ref_time_val;
+	struct aclint_mtimer_data *reference;
+
+	/* Sync-up non-shared MTIME if reference is available */
+	if (mt->has_shared_mtime || !mt->time_delta_reference)
+		return;
+
+	reference = mt->time_delta_reference;
+	mt_time_val = (void *)mt->mtime_addr;
+	ref_time_val = (void *)reference->mtime_addr;
+	if (!atomic_raw_xchg_ulong(&mt->time_delta_computed, 1)) {
+		v1 = mt->time_rd(mt_time_val);
+		mv = reference->time_rd(ref_time_val);
+		v2 = mt->time_rd(mt_time_val);
+		delta = mv - ((v1 / 2) + (v2 / 2));
+		mt->time_wr(false, mt->time_rd(mt_time_val) + delta,
+			    mt_time_val);
+	}
+
+}
+
+void aclint_mtimer_set_reference(struct aclint_mtimer_data *mt,
+				 struct aclint_mtimer_data *ref)
+{
+	if (!mt || !ref || mt == ref)
+		return;
+
+	mt->time_delta_reference = ref;
+	mt->time_delta_computed = 0;
+}
+
 int aclint_mtimer_warm_init(void)
 {
-	u64 v1, v2, mv;
+	u64 *mt_time_cmp;
 	u32 target_hart = current_hartid();
-	struct aclint_mtimer_data *reference;
-	u64 *mt_time_val, *mt_time_cmp, *ref_time_val;
 	struct aclint_mtimer_data *mt = mtimer_hartid2data[target_hart];
 
 	if (!mt)
 		return SBI_ENODEV;
 
-	/*
-	 * Compute delta if reference available
-	 *
-	 * We deliberately compute time_delta in warm init so that time_delta
-	 * is computed on a HART which is going to use given MTIMER. We use
-	 * atomic flag timer_delta_computed to ensure that only one HART does
-	 * time_delta computation.
-	 */
-	if (mt->time_delta_reference) {
-		reference = mt->time_delta_reference;
-		mt_time_val = (void *)mt->mtime_addr;
-		ref_time_val = (void *)reference->mtime_addr;
-		if (!atomic_raw_xchg_ulong(&mt->time_delta_computed, 1)) {
-			v1 = mt->time_rd(mt_time_val);
-			mv = reference->time_rd(ref_time_val);
-			v2 = mt->time_rd(mt_time_val);
-			mt->time_delta = mv - ((v1 / 2) + (v2 / 2));
-		}
-	}
+	/* Sync-up MTIME register */
+	aclint_mtimer_sync(mt);
 
 	/* Clear Time Compare */
 	mt_time_cmp = (void *)mt->mtimecmp_addr;
@@ -173,9 +188,7 @@ int aclint_mtimer_cold_init(struct aclint_mtimer_data *mt,
 		return SBI_EINVAL;
 
 	/* Initialize private data */
-	mt->time_delta_reference = reference;
-	mt->time_delta_computed = 0;
-	mt->time_delta = 0;
+	aclint_mtimer_set_reference(mt, reference);
 	mt->time_rd = mtimer_time_rd32;
 	mt->time_wr = mtimer_time_wr32;
 

lib/utils/timer/fdt_timer_mtimer.c

@@ -17,19 +17,18 @@
 
 static unsigned long mtimer_count = 0;
 static struct aclint_mtimer_data mtimer[MTIMER_MAX_NR];
+static struct aclint_mtimer_data *mt_reference = NULL;
 
 static int timer_mtimer_cold_init(void *fdt, int nodeoff,
 				  const struct fdt_match *match)
 {
-	int rc;
+	int i, rc;
 	unsigned long offset, addr[2], size[2];
-	struct aclint_mtimer_data *mt, *mtmaster = NULL;
+	struct aclint_mtimer_data *mt;
 
 	if (MTIMER_MAX_NR <= mtimer_count)
 		return SBI_ENOSPC;
 	mt = &mtimer[mtimer_count];
-	if (0 < mtimer_count)
-		mtmaster = &mtimer[0];
 
 	rc = fdt_parse_aclint_node(fdt, nodeoff, true,
 				   &addr[0], &size[0], &addr[1], &size[1],
@@ -37,6 +36,7 @@ static int timer_mtimer_cold_init(void *fdt, int nodeoff,
 	if (rc)
 		return rc;
 	mt->has_64bit_mmio = true;
+	mt->has_shared_mtime = false;
 
 	if (match->data) { /* SiFive CLINT */
 		/* Set CLINT addresses */
@@ -63,10 +63,42 @@ static int timer_mtimer_cold_init(void *fdt, int nodeoff,
 			mt->has_64bit_mmio = false;
 	}
 
-	rc = aclint_mtimer_cold_init(mt, mtmaster);
+	/* Check if MTIMER device has shared MTIME address */
+	mt->has_shared_mtime = false;
+	for (i = 0; i < mtimer_count; i++) {
+		if (mtimer[i].mtime_addr == mt->mtime_addr) {
+			mt->has_shared_mtime = true;
+			break;
+		}
+	}
+
+	/* Initialize the MTIMER device */
+	rc = aclint_mtimer_cold_init(mt, mt_reference);
 	if (rc)
 		return rc;
 
+	/*
+	 * Select first MTIMER device with no associated HARTs as our
+	 * reference MTIMER device. This is only a temporary strategy
+	 * of selecting reference MTIMER device. In future, we might
+	 * define an optional DT property or some other mechanism to
+	 * help us select the reference MTIMER device.
+	 */
+	if (!mt->hart_count && !mt_reference) {
+		mt_reference = mt;
+		/*
+		 * Set reference for already propbed MTIMER devices
+		 * with non-shared MTIME
+		 */
+		for (i = 0; i < mtimer_count; i++)
+			if (!mtimer[i].has_shared_mtime)
+				aclint_mtimer_set_reference(&mtimer[i], mt);
+	}
+
+	/* Explicitly sync-up MTIMER devices not associated with any HARTs */
+	if (!mt->hart_count)
+		aclint_mtimer_sync(mt);
+
 	mtimer_count++;
 	return 0;
 }