From a3969eea54a8114fe8957036048f4f6a8028739d Mon Sep 17 00:00:00 2001
From: Matheus <matheusuky@gmail.com>
Date: Sat, 22 Apr 2023 19:21:30 -0300
Subject: [PATCH] kernel: initial hpet support

---
 kernel-src/arch/x86-64/hpet.c         | 55 +++++++++++++++++++++++++++
 kernel-src/arch/x86-64/main.c         |  2 +
 kernel-src/include/time.h             | 11 ++++++
 kernel-src/include/x86-64/arch/acpi.h | 18 +++++++++
 kernel-src/include/x86-64/arch/hpet.h | 12 ++++++
 5 files changed, 98 insertions(+)
 create mode 100644 kernel-src/arch/x86-64/hpet.c
 create mode 100644 kernel-src/include/time.h
 create mode 100644 kernel-src/include/x86-64/arch/hpet.h

diff --git a/kernel-src/arch/x86-64/hpet.c b/kernel-src/arch/x86-64/hpet.c
new file mode 100644
index 00000000..113974d5
--- /dev/null
+++ b/kernel-src/arch/x86-64/hpet.c
@@ -0,0 +1,55 @@
+#include <arch/acpi.h>
+#include <time.h>
+#include <logging.h>
+#include <arch/hpet.h>
+#include <kernel/vmm.h>
+
+#define HPET_REG_CAPS 0
+#define HPET_REG_CONFIG 2
+#define HPET_REG_INTSTATUS 4
+#define HPET_REG_COUNTER 0x1e
+
+#define CAP_FSPERTICK(x) (((x) >> 32) & 0xffffffff)
+
+// XXX there might be several hpets in a system.
+static volatile uint64_t *hpet;
+static time_t ticksperus;
+
+static uint64_t read64(int reg) {
+	return hpet[reg];
+}
+
+static void write64(int reg, uint64_t v) {
+	hpet[reg] = v;
+}
+
+void arch_hpet_waitticks(time_t ticks) {
+	uint64_t target = read64(HPET_REG_COUNTER) + ticks;
+	while (target > read64(HPET_REG_COUNTER)) asm volatile("pause");
+}
+
+void arch_hpet_waitus(time_t us) {
+	arch_hpet_waitticks(us * ticksperus);
+}
+
+bool arch_hpet_exists() {
+	return arch_acpi_findtable("HPET", 0) != NULL;
+}
+
+void arch_hpet_init() {
+	__assert(arch_hpet_exists());
+	hpet_t *table = arch_acpi_findtable("HPET", 0);
+	printf("hpet%lu: %lu bits %lu comparators\n", table->hpetnum, 32 + table->countersize * 32, table->comparatorcount);
+	__assert(table->countersize); // XXX not rely on hpet being 64 bits
+	__assert(table->addrid == 0);
+	__assert((table->addr & PAGE_SIZE) == 0);
+	hpet = vmm_map(NULL, PAGE_SIZE, VMM_FLAGS_PHYSICAL, ARCH_MMU_FLAGS_READ | ARCH_MMU_FLAGS_WRITE | ARCH_MMU_FLAGS_NOEXEC, (void *)table->addr);
+	__assert(hpet);
+	ticksperus = 1000000000 / CAP_FSPERTICK(read64(HPET_REG_CAPS));
+	printf("hpet%lu: %lu ticks per us (%lu fs per tick)\n", table->hpetnum, ticksperus, CAP_FSPERTICK(read64(HPET_REG_CAPS)));
+	__assert(ticksperus);
+
+	write64(HPET_REG_CONFIG, 0);
+	write64(HPET_REG_COUNTER, 0);
+	write64(HPET_REG_CONFIG, 1);
+}
diff --git a/kernel-src/arch/x86-64/main.c b/kernel-src/arch/x86-64/main.c
index ef786a40..fa5eec79 100644
--- a/kernel-src/arch/x86-64/main.c
+++ b/kernel-src/arch/x86-64/main.c
@@ -11,6 +11,7 @@
 #include <kernel/alloc.h>
 #include <arch/acpi.h>
 #include <arch/apic.h>
+#include <arch/hpet.h>
 
 static cpu_t bsp_cpu;
 
@@ -29,5 +30,6 @@ void kernel_entry() {
 	arch_acpi_init();
 	arch_apic_init();
 	arch_apic_initap();
+	arch_hpet_init();
 	__assert(!"kernel entry end");
 }
diff --git a/kernel-src/include/time.h b/kernel-src/include/time.h
new file mode 100644
index 00000000..cbfa12a5
--- /dev/null
+++ b/kernel-src/include/time.h
@@ -0,0 +1,11 @@
+#ifndef _TIME_H
+#define _TIME_H
+
+typedef long time_t;
+
+typedef struct {
+	time_t s;
+	time_t ns;
+} timespec_t;
+
+#endif
diff --git a/kernel-src/include/x86-64/arch/acpi.h b/kernel-src/include/x86-64/arch/acpi.h
index 28d47077..26ca91e6 100644
--- a/kernel-src/include/x86-64/arch/acpi.h
+++ b/kernel-src/include/x86-64/arch/acpi.h
@@ -45,6 +45,24 @@ typedef struct {
 	uint32_t flags;
 } __attribute__((packed)) madt_t;
 
+typedef struct {
+	sdtheader_t header;
+	uint8_t hwrev;
+	uint8_t comparatorcount:5;
+	uint8_t countersize:1;
+	uint8_t reserved:1;
+	uint8_t legacy_replacement:1;
+	uint16_t pcivendor;
+	uint8_t addrid;
+	uint8_t bitwidth;
+	uint8_t bitoffset;
+	uint8_t reserved2;
+	uint64_t addr;
+	uint8_t hpetnum;
+	uint16_t mintick;
+	uint8_t pageprot;
+} __attribute__((packed)) hpet_t;
+
 #define ACPI_MADT_TYPE_LAPIC 0
 #define ACPI_MADT_TYPE_IOAPIC 1
 #define ACPI_MADT_TYPE_OVERRIDE 2
diff --git a/kernel-src/include/x86-64/arch/hpet.h b/kernel-src/include/x86-64/arch/hpet.h
new file mode 100644
index 00000000..1d02040b
--- /dev/null
+++ b/kernel-src/include/x86-64/arch/hpet.h
@@ -0,0 +1,12 @@
+#ifndef _HPET_H
+#define _HPET_h
+
+#include <stdbool.h>
+#include <time.h>
+
+void arch_hpet_waitticks(time_t ticks);
+void arch_hpet_waitus(time_t us);
+bool arch_hpet_exists();
+void arch_hpet_init();
+
+#endif