risc-v: Implement benchmark timestamp

Implements timestamp function used by benchmark logging utilities.

Signed-off-by: Curtis Millar <curtis.millar@data61.csiro.au>
Signed-off-by: Curtis Millar <curtis@curtism.me>

include/arch/riscv/arch/32/mode/hardware.h

@@ -79,5 +79,24 @@ static inline uint64_t riscv_read_time(void)
     return ((uint64_t)((uint64_t) nH1 << 32)) | (nL);
 }
 
+static inline uint64_t riscv_read_cycle(void)
+{
+    uint32_t nH1, nL, nH2;
+    asm volatile(
+        "rdcycleh %0\n"
+        "rdcycle  %1\n"
+        "rdcycleh %2\n"
+        : "=r"(nH1), "=r"(nL), "=r"(nH2));
+    if (nH1 != nH2) {
+        /* Ensure that the time is correct if there is a rollover in the
+         * high bits between reading the low and high bits. */
+        asm volatile(
+            "rdcycle  %0\n"
+            : "=r"(nL));
+        nH1 = nH2;
+    }
+    return ((uint64_t)((uint64_t) nH1 << 32)) | (nL);
+}
+
 #endif /* __ASSEMBLER__ */
 

include/arch/riscv/arch/64/mode/hardware.h

@@ -121,5 +121,14 @@ static inline uint64_t riscv_read_time(void)
     return n;
 }
 
+static inline uint64_t riscv_read_cycle(void)
+{
+    uint64_t n;
+    asm volatile(
+        "rdcycle %0"
+        : "=r"(n));
+    return n;
+}
+
 #endif /* __ASSEMBLER__ */
 

include/arch/riscv/arch/benchmark.h

@@ -9,8 +9,12 @@
 
 #include <config.h>
 #include <arch/object/structures.h>
+#include <mode/hardware.h>
 
 #ifdef CONFIG_ENABLE_BENCHMARK
-#error "RISC-V doesn't support timestamp() function yet"
+static inline timestamp_t timestamp(void)
+{
+    return riscv_read_cycle();
+}
 #endif /* CONFIG_ENABLE_BENCHMARK */
 

include/arch/riscv/arch/types.h

@@ -33,6 +33,8 @@ typedef node_id_t seL4_NodeId;
 typedef paddr_t seL4_PAddr;
 typedef dom_t seL4_Domain;
 
+typedef uint64_t timestamp_t;
+
 #define wordBits BIT(wordRadix)
 
 typedef struct kernel_frame {