From 0c75ed9fb14275603b478c5bbd96bcd4d3f982e6 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 21 Sep 2025 01:02:53 -0400
Subject: kern: clkdev: Add callback to get elapsed time

Add new clock device callback to get the elapsed time from the timer
being initialized, in microseconds.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 src/sys/arch/amd64/io/hpet.c | 23 ++++++++++++++++++++++-
 src/sys/include/os/clkdev.h  |  5 ++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/sys/arch/amd64/io/hpet.c b/src/sys/arch/amd64/io/hpet.c
index 36f19a8..d733d9b 100644
--- a/src/sys/arch/amd64/io/hpet.c
+++ b/src/sys/arch/amd64/io/hpet.c
@@ -42,6 +42,9 @@
 #include <acpi/tables.h>
 #include <machine/hpet.h>
 
+#define FSEC_PER_SECOND 1000000000000000ULL
+#define USEC_PER_SECOND 1000000ULL
+
 #define HPET_REG_CAPS               0x00
 #define HPET_GENERAL_CONFIG         0x10
 #define HPET_REG_MAIN_COUNTER       0xF0
@@ -118,6 +121,23 @@ hpet_msleep(size_t ms)
     return hpet_sleep(ms, 1000000000000);
 }
 
+/*
+ * Get time since init in usec
+ */
+static size_t
+hpet_time_usec(void)
+{
+    uint64_t period, freq, caps;
+    uint64_t counter;
+
+    caps = hpet_read(HPET_REG_CAPS);
+    period = CAP_CLK_PERIOD(caps);
+    freq = FSEC_PER_SECOND / period;
+
+    counter = hpet_read(HPET_REG_MAIN_COUNTER);
+    return (counter * USEC_PER_SECOND) / freq;
+}
+
 /*
  * Initialize the HPET
  */
@@ -162,8 +182,9 @@ hpet_init(void)
 
     /* Initialize as clock device */
     clkdev.name = "IA-PC HPET";
-    clkdev.attr = CLKDEV_MSLEEP;
+    clkdev.attr = CLKDEV_MSLEEP | CLKDEV_GET_USEC;
     clkdev.msleep = hpet_msleep;
+    clkdev.get_time_usec = hpet_time_usec;
     if (clkdev_register(&clkdev) < 0) {
         printf("hpet_init: could not register clock device\n");
         return -1;
diff --git a/src/sys/include/os/clkdev.h b/src/sys/include/os/clkdev.h
index 1f776cd..e70d91b 100644
--- a/src/sys/include/os/clkdev.h
+++ b/src/sys/include/os/clkdev.h
@@ -34,7 +34,8 @@
 #include <sys/param.h>
 
 /* Clock attributes */
-#define CLKDEV_MSLEEP BIT(0)    /* Has msleep() */
+#define CLKDEV_MSLEEP    BIT(0)  /* Has msleep() */
+#define CLKDEV_GET_USEC  BIT(1)  /* Get elapsed usec */
 
 #define MAX_CLKDEV 4
 
@@ -44,11 +45,13 @@
  *
  * @name: Name of clock
  * @msleep: Sleep for 'n' msec
+ * @get_time_usec: Get time since init in microseconds
  * @attr: Attribute mask
  */
 struct clkdev {
     const char *name;
     int(*msleep)(size_t ms);
+    size_t(*get_time_usec)(void);
     uint16_t attr;
 };
 
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