From 29de9befc914cf9e9db0e85ad8bb6ede828e157d Mon Sep 17 00:00:00 2001
From: "Chloe M." <chloe@mensia.org>
Date: Fri, 26 Jun 2026 14:05:27 -0500
Subject: [PATCH] stos/amd64: hpet: Implement HPET register checking

Signed-off-by: Chloe M. <chloe@mensia.org>
---
 paw/stos/arch/amd64/platform/hpet.c | 64 +++++++++++++++++++++++++++++
 paw/stos/head/arch/amd64/hpetreg.h  |  3 ++
 2 files changed, 67 insertions(+)

diff --git a/paw/stos/arch/amd64/platform/hpet.c b/paw/stos/arch/amd64/platform/hpet.c
index cd867ea..b707a7d 100644
--- a/paw/stos/arch/amd64/platform/hpet.c
+++ b/paw/stos/arch/amd64/platform/hpet.c
@@ -7,18 +7,64 @@
  */
 
 #include <machine/hpet.h>
+#include <machine/hpetreg.h>
 #include <drivers/acpi/tables.h>
 #include <drivers/acpi/acpi.h>
+#include <hal/mmio.h>
+#include <mm/vmm.h>
 #include <ke/knot.h>
 #include <ex/trace.h>
 
 #define DTRACE(Fmt, ...) \
     TRACE("[ HPET ]: " Fmt, ##__VA_ARGS__)
 
+static VOID *MMIOBase = NULL;
+
+/*
+ * Write a 64-bit value to an HPET register
+ *
+ * @Register: Register to write to
+ * @Value:    Value to write
+ */
+static VOID
+HpetWriteq(UCHAR Register, UQUAD Value)
+{
+    VOID *RegBase;
+
+    if (MMIOBase == NULL) {
+        return;
+    }
+
+    RegBase = PTR_OFFSET(MMIOBase, Register);
+    MMIOWrite64(MMIOBase, Value);
+}
+
+/*
+ * Read a 64-bit value from an HPET register
+ *
+ * @Register:  Register to read from
+ */
+static UQUAD
+HpetReadq(UCHAR Register)
+{
+    VOID *RegBase;
+
+    if (MMIOBase == NULL) {
+        return 0;
+    }
+
+    RegBase = PTR_OFFSET(MMIOBase, Register);
+    return MMIORead64(RegBase);
+}
+
 VOID
 MdHpetInit(VOID)
 {
     ACPI_HPET *Hpet;
+    UQUAD GeneralCap;
+    ULONG ClkPeriod;
+    UCHAR RevId;
+    const ACPI_GAS *Gas;
 
     Hpet = AcpiQuery("HPET");
     if (Hpet == NULL) {
@@ -32,4 +78,22 @@ MdHpetInit(VOID)
     DTRACE("detected hpet with pci vendor id : %x\n", Hpet->PciVendorId);
     DTRACE("counter size : %d\n", Hpet->CounterSize);
     DTRACE("minimum tick : %d\n", Hpet->MinimumTick);
+
+    /* Obtain the MMIO base address */
+    Gas = &Hpet->Gas;
+    MMIOBase = PMA_TO_VMA(Gas->Address);
+
+    GeneralCap = HpetReadq(HPET_GENERAL_CAP);
+    ClkPeriod = (GeneralCap >> HPET_PERIOD_SHIFT) & HPET_PERIOD_MASK;
+    RevId = GeneralCap & 0xFF;
+    DTRACE("counter clk period : %d\n", ClkPeriod);
+
+    /*
+     * Verify that the clock period and the revision ID are not
+     * garbage values.
+     */
+    if (ClkPeriod > HPET_MAX_CLK_PERIOD)
+        KeKnot(KNOT_MISC, "hpet: bad counter clk period\n");
+    if (RevId == 0)
+        KeKnot(KNOT_MISC, "hpet: bad revision id, must not be zero\n");
 }
diff --git a/paw/stos/head/arch/amd64/hpetreg.h b/paw/stos/head/arch/amd64/hpetreg.h
index f57bcfc..fc4b530 100644
--- a/paw/stos/head/arch/amd64/hpetreg.h
+++ b/paw/stos/head/arch/amd64/hpetreg.h
@@ -26,4 +26,7 @@
 #define HPET_GCONF_EN BIT(0)
 #define HPET_LEG_RT   BIT(1)
 
+/* Max constants */
+#define HPET_MAX_CLK_PERIOD 0x5F5E100
+
 #endif  /* !_MACHINE_HPETREG_H_ */