Documentation

documentation/5 - acpi.md

@@ -0,0 +1,27 @@
+# Parsing ACPI information
+
+> - [ACPI Specification](https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf)
+
+ACPI is a standard for controlling things like power and temperatures in computers. It's also useful for getting some information about the machine, such as number of processors - which is what Mittos will be using it for (at least at first).
+
+The bootloader will find the Root System Descriptor Pointer and provide it in a boot tag. Then the data just needs to be parsed.
+
+The RSDP contains a pointer to the Root System Descriptor Table which contains pointers to more System Descriptor Tables.
+
+The important fields for parsing a System Descript Tables are as follows:
+```c
+struct sdt {
+    char signature[4];
+    uint32_t length;
+    uint8_t _[28];
+    uint32_t data[];
+}__attribute__((packed));
+```
+
+So I step through the pointers in the RSDT data field until I find an SDT with signature "APIC". That should contain the Multiple APIC Description Table.
+
+The MADT in turn contains a number of fields with information - among other things - about Processor Local APICs, I/O Apics and IRQ redirections.
+Those are things I may be interested in, and therefore store in some global data structures.
+
+## Relevant files
+- `src/kernel/cpu/acpi.c`

src/kernel/cpu/acpi.c

@@ -1,5 +1,5 @@
 #include <cpu.h>
-#include <multiboot.h>
+
 #include <memory.h>
 #include <string.h>
 #include <debug.h>
@@ -12,108 +12,100 @@ struct rsdp { // 5.2.5.3
     char OEMID[6];
     uint8_t revision;
     uint32_t rsdt_p;
-    uint32_t length; // only if revision >= 2
+    uint8_t _[14]; // Fields for revision >= 2
-    uint64_t xsdt_p; // only if revision >= 2
-    uint8_t checksum2; // only if revision >= 2
-    uint8_t reserved[3]; // only if revision >= 2
 }__attribute__((packed));
 
-struct sdt_header { // 5.2.6
+struct sdt {
     char signature[4];
     uint32_t length;
-    uint8_t revision;
+    uint8_t _[28];
-    uint8_t checksum;
+    uint32_t data[];
-    char OEMID[6];
-    char OEMtable[8];
-    uint32_t OEMrevision;
-    uint32_t creatorID;
-    uint32_t creatorRevision;
-    uint8_t data[];
 }__attribute__((packed));
 
-struct madt_header { // 5.2.12
+
-    uint32_t controllerAddress;
+// MADT (5.2.12)
-    uint32_t flags;
+#define MADT_TYPE_LAPIC 0
-    uint8_t fields[];
+#define MADT_TYPE_IOAPIC 1
-}__attribute__((packed));
+#define MADT_TYPE_ISO 2
 
 struct madt_field {
     uint8_t type;
     uint8_t length;
-    uint8_t data[];
+    union {
-}__attribute__((packed));
+        // Processor Local APIC (5.2.12.2)
-
+        struct {
-// MADT field type: 0
-#define MADT_TYPE_LAPIC 0
-struct madt_data_lapic { // 5.2.12.2
             uint8_t id;
             uint8_t apic;
             uint32_t flags;
-}__attribute__((packed));
+        }__attribute__((packed)) lapic;
-
+        // I/O APIC (5.2.12.3)
-// MADT field type: 1
+        struct {
-#define MADT_TYPE_IOAPIC 1
-struct madt_data_ioapic { // 5.2.12.3
             uint8_t id;
             uint8_t reserved;
             uint32_t address;
             uint32_t base;
-}__attribute__((packed));
+        }__attribute__((packed)) ioapic;
-
+        // Interrupt source override (5.2.12.5)
-// MADT field type: 2
+        struct {
-#define MADT_TYPE_ISO 2
-struct madt_data_iso { // 5.2.12.5
             uint8_t bus;
             uint8_t source;
             uint32_t interrupt;
             uint16_t flags;
+        }__attribute__((packed)) iso;
+    };
+}__attribute__((packed));
+
+struct madt_header {
+    uint32_t controllerAddress;
+    uint32_t flags;
+    struct madt_field fields[];
 }__attribute__((packed));
 
 
-void acpi_parse() {
+static void madt_parse(struct madt_header *madt, size_t length)
+{
     int cpu_i=0;
-
-    struct rsdp *rsdp = kernel_boot_data.rsdp;
-    struct sdt_header *rsdt = P2V(rsdp->rsdt_p);
-
-    uint32_t *table = (void *)rsdt->data;
-    int entries = (rsdt->length - sizeof(struct sdt_header))/sizeof(uint32_t);
-    for(int i = 0; i < entries; i++) {
-        struct sdt_header *h = P2V(table[i]);
-        if(h->length == 0) continue;
-
-        if(!strncmp(h->signature, "APIC", 4)) { // 5.2.12
-            struct madt_header *madt = P2V(h->data);
     for(
-                struct madt_field *f = (void *)madt->fields;
+        struct madt_field *f = madt->fields;
-                (size_t)f <= (size_t)h + h->length;
+        (size_t)f <= (size_t)madt + length;
         f = incptr(f, f->length)
     ) {
         switch(f->type) {
             case MADT_TYPE_LAPIC: {
-                        struct madt_data_lapic *lapic = (void *)f->data;
                 struct cpu *cpu = P2V(pmm_alloc());
                 cpus[cpu_i++] = cpu;
-                        cpu->id = lapic->id;
+                cpu->id = f->lapic.id;
-                        cpu->apic_id = lapic->apic;
+                cpu->apic_id = f->lapic.apic;
-                        cpu->flags = lapic->flags;
+                cpu->flags = f->lapic.flags;
                 break;
             }
             case MADT_TYPE_IOAPIC: {
-                        struct madt_data_ioapic *_ioapic = (void *)f->data;
+                ioapic.id = f->ioapic.id;
-                        ioapic.id = _ioapic->id;
+                ioapic.addr = f->ioapic.address;
-                        ioapic.addr = _ioapic->address;
+                ioapic.base = f->ioapic.base;
-                        ioapic.base = _ioapic->base;
                 break;
             }
             case MADT_TYPE_ISO: {
-                        struct madt_data_iso *iso = (void *)f->data;
+                irq_redirects[f->iso.source] = f->iso.interrupt;
-                        irq_redirects[iso->source] = iso->interrupt;
                 break;
             }
             default:
         }
     }
 }
+
+void acpi_parse(void *_rsdp) {
+    struct rsdp *rsdp = _rsdp;
+
+    struct sdt *rsdt = P2V(rsdp->rsdt_p);
+    int rsdt_entries = (rsdt->length - sizeof(struct sdt))/sizeof(uint32_t);
+
+    for(int i = 0; i < rsdt_entries; i++) {
+        struct sdt *h = P2V(rsdt->data[i]);
+        if(h->length == 0) continue;
+
+        if(!strncmp(h->signature, "APIC", 4)) { // 5.2.12
+            madt_parse(P2V(h->data), h->length - sizeof(struct sdt));
+        }
     }
 }

src/kernel/cpu/cpu.c

@@ -1,6 +1,7 @@
 #include <cpu.h>
 #include <cpu/interrupts.h>
 #include <ports.h>
+#include <multiboot.h>
 
 struct cpu *cpus[16];
 struct ioapic ioapic = {0,0,0};
@@ -31,7 +32,7 @@ void early_cpu_init() {
 }
 
 void cpu_init() {
-    acpi_parse();
+    acpi_parse(kernel_boot_data.rsdp);
     pic_disable();
     apic_init();
     ioapic_init();

src/kernel/include/cpu.h

@@ -33,7 +33,7 @@ uint64_t read_msr(uint32_t);
 uint64_t write_msr(uint32_t msr, uint64_t value);
 
 // cpu/acpi.c
-void acpi_parse();
+void acpi_parse(void *_rsdp);
 
 // cpu/apic.c
 void apic_init();