1 files changed, 84 insertions, 0 deletions
diff --git a/src/boot/efi/ticks.c b/src/boot/efi/ticks.c
new file mode 100644
index 0000000..889980a
--- /dev/null
+++ b/src/boot/efi/ticks.c
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <efi.h>
+#include <efilib.h>
+
+#include "ticks.h"
+#include "util.h"
+
+#ifdef __x86_64__
+static uint64_t ticks_read(void) {
+        uint64_t a, d;
+
+        /* The TSC might or might not be virtualized in VMs (and thus might not be accurate or start at zero
+         * at boot), depending on hypervisor and CPU functionality. If it's not virtualized it's not useful
+         * for keeping time, hence don't attempt to use it. */
+        if (in_hypervisor())
+                return 0;
+
+        __asm__ volatile ("rdtsc" : "=a" (a), "=d" (d));
+        return (d << 32) | a;
+}
+#elif defined(__i386__)
+static uint64_t ticks_read(void) {
+        uint64_t val;
+
+        if (in_hypervisor())
+                return 0;
+
+        __asm__ volatile ("rdtsc" : "=A" (val));
+        return val;
+}
+#elif defined(__aarch64__)
+static uint64_t ticks_read(void) {
+        uint64_t val;
+        asm volatile("mrs %0, cntvct_el0" : "=r"(val));
+        return val;
+}
+#else
+static uint64_t ticks_read(void) {
+        return 0;
+}
+#endif
+
+#if defined(__aarch64__)
+static uint64_t ticks_freq(void) {
+        uint64_t freq;
+        asm volatile("mrs %0, cntfrq_el0" : "=r"(freq));
+        return freq;
+}
+#else
+/* count TSC ticks during a millisecond delay */
+static uint64_t ticks_freq(void) {
+        uint64_t ticks_start, ticks_end;
+        static uint64_t cache = 0;
+
+        if (cache != 0)
+                return cache;
+
+        ticks_start = ticks_read();
+        BS->Stall(1000);
+        ticks_end = ticks_read();
+
+        if (ticks_end < ticks_start) /* Check for an overflow (which is not that unlikely, given on some
+                                      * archs the value is 32bit) */
+                return 0;
+
+        cache = (ticks_end - ticks_start) * 1000UL;
+        return cache;
+}
+#endif
+
+uint64_t time_usec(void) {
+        uint64_t ticks, freq;
+
+        ticks = ticks_read();
+        if (ticks == 0)
+                return 0;
+
+        freq = ticks_freq();
+        if (freq == 0)
+                return 0;
+
+        return 1000UL * 1000UL * ticks / freq;
+}