stos: acpi: Add ACPI impl groundwork

Signed-off-by: Chloe M. <chloe@mensia.org>

paw/stos/drivers/acpi/acpi.c

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: ACPI init
+ * Author:      Chloe M.
+ */
+
+#include <drivers/acpi/acpi.h>
+#include <drivers/acpi/tables.h>
+#include <ex/trace.h>
+#include <mm/vmm.h>
+#include <ke/bpal.h>
+#include <ke/knot.h>
+#include <string.h>
+
+#define DTRACE(Fmt, ...) \
+    TRACE("[ ACPI ]: " Fmt, ##__VA_ARGS__)
+
+static ACPI_RSDP *Rsdp;
+static ACPI_ROOT_SDT *RootSdt;
+static USIZE RootSdtEntries;
+
+static VOID
+AcpiPrintVendor(VOID)
+{
+    UCHAR Revision;
+
+    /*
+     * On certain emulators this may become zero, just bump it up to
+     * one because its behaviors are the same.
+     */
+    Revision = Rsdp->Revision;
+    if (Revision == 0) {
+        ++Revision;
+    }
+
+    DTRACE("detected acpi %d.0 by %.6s\n", Revision, Rsdp->Oemid);
+}
+
+static VOID
+RsdpVerify(VOID)
+{
+    UCHAR Checksum = 0;
+    USIZE Idx;
+
+    for (Idx = 0; Idx < Rsdp->Length; ++Idx) {
+        Checksum += ((UCHAR *)Rsdp)[Idx];
+    }
+
+    if ((Checksum & 0xFF) != 0) {
+        KeKnot(
+            KNOT_BAD_CHECKSUM,
+            "Got bad checksum %x for ACPI RSDP\n",
+            Checksum
+        );
+    }
+
+    DTRACE("checksum ok\n");
+}
+
+VOID *
+AcpiQuery(const CHAR *Signature)
+{
+    BOOLEAN IsMatch;
+    ACPI_HEADER *Header;
+    UPTR Pma;
+    USIZE Idx;
+
+    if (Signature == NULL) {
+        return NULL;
+    }
+
+    for (Idx = 0; Idx < RootSdtEntries; ++Idx) {
+        Pma = (UPTR)RootSdt->Tables[Idx];
+        Header = (ACPI_HEADER *)PMA_TO_VMA(Pma);
+        IsMatch = !RtlMemCmp(
+            Header->Signature,
+            Signature,
+            sizeof(Header->Signature)
+        );
+
+        if (IsMatch) {
+            return (VOID *)Header;
+        }
+    }
+
+    return NULL;
+}
+
+VOID
+AcpiInit(VOID)
+{
+    BPAL_HANDLE BpalHandle;
+
+    KeBpalGetHandle(&BpalHandle);
+    Rsdp = BpalHandle.RsdpBase;
+    AcpiPrintVendor();
+    RsdpVerify();
+
+    /* Select the correct root sdt */
+    if (Rsdp->Revision < 2) {
+        DTRACE("using rsdt as root sdt\n");
+        RootSdt = PMA_TO_VMA((UPTR)Rsdp->RsdtAddr);
+        RootSdtEntries = (RootSdt->Header.Length - sizeof(RootSdt->Header)) / 4;
+    } else {
+        DTRACE("using xsdt as root sdt\n");
+        RootSdt = PMA_TO_VMA((UPTR)Rsdp->XsdtAddr);
+        RootSdtEntries = (RootSdt->Header.Length - sizeof(RootSdt->Header)) / 8;
+    }
+}

paw/stos/head/drivers/acpi/acpi.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: ACPI driver
+ * Author:      Chloe M.
+ */
+
+#ifndef _ACPI_ACPI_H_
+#define _ACPI_ACPI_H_ 1
+
+#include <stdef.h>
+
+/*
+ * Initialize ACPI
+ */
+VOID AcpiInit(VOID);
+
+/*
+ * Query an ACPI structure
+ *
+ * @Signature: Signature to query for
+ *
+ * Returns the virtual structure base on success, otherwise
+ * NULL on failure.
+ */
+VOID *AcpiQuery(const CHAR *Signature);
+
+#endif  /* !_ACPI_ACPI_H_ */

paw/stos/init/init.c

@@ -14,6 +14,7 @@
 #include <hal/serial.h>
 #include <hal/kpcr.h>
 #include <drivers/bootvid/fbio.h>
+#include <drivers/acpi/acpi.h>
 #include <mm/pmm.h>
 #include <mm/vmm.h>
 #include <stdef.h>
@@ -71,4 +72,7 @@ KiKernelEntry(VOID)
 
     /* Initialize virtual memory */
     MmInitVmm();
+
+    /* Initialize ACPI */
+    AcpiInit();
 }