lib: utils/timer: Optimize current hart scratch access

The address of the local scratch area is stored in each hart's mscratch
CSR. It is more efficient to read the CSR than to compute the address
from the hart ID.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

Author: SiFiveHolland

lib/utils/timer/aclint_mtimer.c

@@ -72,14 +72,10 @@ static u64 mtimer_value(void)
 static void mtimer_event_stop(void)
 {
 	u32 target_hart = current_hartid();
-	struct sbi_scratch *scratch;
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
 	struct aclint_mtimer_data *mt;
 	u64 *time_cmp;
 
-	scratch = sbi_hartid_to_scratch(target_hart);
-	if (!scratch)
-		return;
-
 	mt = mtimer_get_hart_data_ptr(scratch);
 	if (!mt)
 		return;
@@ -92,14 +88,10 @@ static void mtimer_event_stop(void)
 static void mtimer_event_start(u64 next_event)
 {
 	u32 target_hart = current_hartid();
-	struct sbi_scratch *scratch;
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
 	struct aclint_mtimer_data *mt;
 	u64 *time_cmp;
 
-	scratch = sbi_hartid_to_scratch(target_hart);
-	if (!scratch)
-		return;
-
 	mt = mtimer_get_hart_data_ptr(scratch);
 	if (!mt)
 		return;
@@ -155,13 +147,9 @@ int aclint_mtimer_warm_init(void)
 {
 	u64 *mt_time_cmp;
 	u32 target_hart = current_hartid();
-	struct sbi_scratch *scratch;
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
 	struct aclint_mtimer_data *mt;
 
-	scratch = sbi_hartid_to_scratch(target_hart);
-	if (!scratch)
-		return SBI_ENOENT;
-
 	mt = mtimer_get_hart_data_ptr(scratch);
 	if (!mt)
 		return SBI_ENODEV;