kboot: Need to find the ACPI tables

We need to pass the ACPI tables to the laucnhed kernel (at least for x86
and aarch64). Find it using the Linux standard way.

Sponsored by:		Netflix

stand/kboot/kboot.h

@@ -9,6 +9,9 @@
 
 #define DEVT_HOSTDISK 1234
 
+bool has_acpi(void);
+vm_offset_t acpi_rsdp(void);
+
 void do_init(void);
 
 extern const char *hostfs_root;

stand/kboot/main.c

@@ -102,6 +102,50 @@ parse_args(int argc, const char **argv)
 	return (howto);
 }
 
+static vm_offset_t rsdp;
+
+static vm_offset_t
+kboot_rsdp_from_efi(void)
+{
+	char buffer[512 + 1];
+	char *walker, *ep;
+
+	if (!file2str("/sys/firmware/efi/systab", buffer, sizeof(buffer)))
+		return (0);	/* Not an EFI system */
+	ep = buffer + strlen(buffer);
+	walker = buffer;
+	while (walker < ep) {
+		if (strncmp("ACPI20=", walker, 7) == 0)
+			return((vm_offset_t)strtoull(walker + 7, NULL, 0));
+		if (strncmp("ACPI=", walker, 5) == 0)
+			return((vm_offset_t)strtoull(walker + 5, NULL, 0));
+		walker += strcspn(walker, "\n");
+	}
+	return (0);
+}
+
+static void
+find_acpi()
+{
+	rsdp = kboot_rsdp_from_efi();
+#if 0	/* maybe for amd64 */
+	if (rsdp == 0)
+		rsdp = find_rsdp_arch();
+#endif
+}
+
+vm_offset_t
+acpi_rsdp()
+{
+	return (rsdp);
+}
+
+bool
+has_acpi()
+{
+	return rsdp != 0;
+}
+
 int
 main(int argc, const char **argv)
 {
@@ -146,6 +190,11 @@ main(int argc, const char **argv)
 	setenv("LINES", "24", 1);
 	setenv("usefdt", "1", 1);
 
+	/*
+	 * Find acpi, if it exists
+	 */
+	find_acpi();
+
 	interact();			/* doesn't return */
 
 	return (0);