diff --git a/Makefile b/Makefile
index bdc0117..07c9b04 100644
--- a/Makefile
+++ b/Makefile
@@ -370,25 +370,6 @@
 $(call mark_unsupported,$(DEPENDS_ON_RAW_MEM_ACCESS))
 endif
 
-ifeq ($(TARGET_OS), $(filter $(TARGET_OS), Linux Darwin NetBSD OpenBSD))
-FEATURE_FLAGS += -D'USE_IOPL=1'
-else
-FEATURE_FLAGS += -D'USE_IOPL=0'
-endif
-
-ifeq ($(TARGET_OS), $(filter $(TARGET_OS), FreeBSD FreeBSD-glibc DragonFlyBSD))
-FEATURE_FLAGS += -D'USE_DEV_IO=1'
-else
-FEATURE_FLAGS += -D'USE_DEV_IO=0'
-endif
-
-ifeq ($(TARGET_OS), $(filter $(TARGET_OS), Hurd))
-FEATURE_FLAGS += -D'USE_IOPERM=1'
-else
-FEATURE_FLAGS += -D'USE_IOPERM=0'
-endif
-
-
 ###############################################################################
 # Flash chip drivers and bus support infrastructure.
 
diff --git a/hwaccess_x86_io.c b/hwaccess_x86_io.c
index 37b1eb7..3144da2 100644
--- a/hwaccess_x86_io.c
+++ b/hwaccess_x86_io.c
@@ -17,12 +17,25 @@
  */
 
 /*
- * This file implements x86 I/O port permission handling.
+ * This file implements x86 I/O port permission and access handling.
  *
- * For this purpose the platform specific code is encapsuled in two functions
- * and compiled only on the respective platform. `platform_get_io_perms()` is
- * called to get the permissions and `platform_release_io_perms()` is called for
- * releasing those.
+ * The first part of the file defines the platform dependend implementations to
+ * use on each platform. For getting I/O permissions set IO_PORT_PERMISSION to
+ * one of:
+ *   - USE_DUMMY
+ *   - USE_SUN
+ *   - USE_DEVICE
+ *   - USE_IOPERM
+ *   - USE_IOPL
+ * For the IN[B/W/L] and OUT[B/W/L] functions set IO_PORT_FUNCTION to one of:
+ *   - USE_LIBC_TARGET_LAST
+ *   - USE_LIBC_TARGET_FIRST
+ *   - USE_DOS
+ *   - USE_ASM
+ *
+ * The platform specific code for getting I/O permissions consists of two
+ * functions. `platform_get_io_perms()` is called to get
+ * permissions and `platform_release_io_perms()` is called for releasing those.
  */
 
 #include <errno.h>
@@ -31,7 +44,126 @@
 #include "flash.h"
 #include "hwaccess_x86_io.h"
 
-#if defined(__DJGPP__) || defined(__LIBPAYLOAD) /* DJGPP, libpayload */
+/* IO_PORT_FUNCTION */
+#define USE_LIBC_TARGET_LAST	1
+#define USE_LIBC_TARGET_FIRST	2
+#define USE_ASM			3
+#define USE_DOS			4
+
+/* IO_PORT_PERMISSION */
+#define USE_IOPL		5
+#define USE_DEVICE		6
+#define USE_DUMMY		7
+#define USE_SUN			8
+#define USE_IOPERM		9
+
+#if defined(__ANDROID__)
+#include <sys/glibc-syscalls.h>
+
+#define IO_PORT_PERMISSION USE_IOPL
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_LAST
+#endif
+
+#if defined(__linux__) && !defined(__ANDROID__)
+#include <sys/io.h>
+
+#define IO_PORT_PERMISSION USE_IOPL
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_LAST
+#endif
+
+#if defined(__FreeBSD_kernel) && defined(__GLIBC__)
+#include <sys/io.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define IO_PORT_PERMISSION USE_DEVICE
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_LAST
+#endif
+
+#if defined(__FreeBSD__) || defined(__DragonFly__)
+#include <sys/types.h>
+#include <machine/cpufunc.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define IO_PORT_PERMISSION USE_DEVICE
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_FIRST
+#endif
+
+#if defined(__NetBSD__)
+#include <sys/types.h>
+#include <machine/sysarch.h>
+
+#if defined(__i386__)
+#define iopl i386_iopl
+#elif defined(__x86_64__)
+#define iopl x86_64_iopl
+#endif
+
+#define IO_PORT_PERMISSION USE_IOPL
+#define IO_PORT_FUNCTION USE_ASM
+#endif
+
+#if defined(__OpenBSD__)
+#include <sys/types.h>
+#include <machine/sysarch.h>
+
+#if defined(__i386__)
+#define iopl i386_iopl
+#elif defined(__amd64__)
+#define iopl amd64_iopl
+#endif
+
+#define IO_PORT_PERMISSION USE_IOPL
+#define IO_PORT_FUNCTION USE_ASM
+#endif
+
+#if defined(__MACH__) && defined(__APPLE__)
+#include <DirectHW/DirectHW.h>
+
+#define IO_PORT_PERMISSION USE_IOPL
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_LAST
+#endif
+
+#if defined(__DJGPP__)
+#include <pc.h>
+
+#define IO_PORT_PERMISSION USE_DUMMY
+#define IO_PORT_FUNCTION USE_DOS
+#endif
+
+#if defined(__LIBPAYLOAD__)
+#define IO_PORT_PERMISSION USE_DUMMY
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_LAST
+#endif
+
+#if defined(__sun)
+#include <sys/sysi86.h>
+#include <sys/psw.h>
+#include <asm/sunddi.h>
+
+#define IO_PORT_PERMISSION USE_SUN
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_FIRST
+#endif
+
+#if defined(__gnu_hurd__)
+#include <sys/io.h>
+
+#define IO_PORT_PERMISSION USE_IOPERM
+#define IO_PORT_FUNCTION USE_LIBC_TARGET_LAST
+#endif
+
+/* Make sure IO_PORT_PERMISSION and IO_PORT_FUNCTION are set */
+#if IO_PORT_PERMISSION == 0 || IO_PORT_FUNCTION == 0
+#error Unsupported or misconfigured platform.
+#endif
+
+/*
+ * USE_DUMMY
+ * This is for platforms which have no privilege levels.
+ */
+#if IO_PORT_PERMISSION == USE_DUMMY
 static int platform_get_io_perms(void)
 {
 	return 0;
@@ -43,9 +175,11 @@
 }
 #endif
 
-#if defined(__sun) /* SunOS */
-#include <sys/sysi86.h>
-
+/*
+ * USE_SUN
+ * This implementation uses SunOS system call sysi86 to handle I/O port permissions.
+ */
+#if IO_PORT_PERMISSION == USE_SUN
 static int platform_get_io_perms(void)
 {
 	return sysi86(SI86V86, V86SC_IOPL, PS_IOPL);
@@ -58,10 +192,11 @@
 }
 #endif
 
-#if USE_DEV_IO /* FreeBSD, DragonFlyBSD */
-#include <fcntl.h>
-#include <unistd.h>
-
+/*
+ * USE_DEVICE
+ * This implementation uses the virtual /dev/io file to handle I/O Port permissions.
+ */
+#if IO_PORT_PERMISSION == USE_DEVICE
 int io_fd;
 
 static int platform_get_io_perms(void)
@@ -77,9 +212,11 @@
 }
 #endif
 
-#if USE_IOPERM /* GNU Hurd */
-#include <sys/io.h>
-
+/*
+ * USE_IOPERM
+ * This implementation uses the ioperm system call to handle I/O port permissions.
+ */
+#if IO_PORT_PERMISSION == USE_IOPERM
 static int platform_get_io_perms(void)
 {
 	return ioperm(0, 65536, 1);
@@ -92,7 +229,11 @@
 }
 #endif
 
-#if USE_IOPL /* Linux, Darwin, NetBSD, OpenBSD */
+/*
+ * USE_IOPL
+ * This implementation uses the iopl system call to handle I/O port permissions.
+ */
+#if IO_PORT_PERMISSION == USE_IOPL
 static int platform_get_io_perms(void)
 {
 	return iopl(3);
@@ -134,3 +275,145 @@
 #endif
 	return 1;
 }
+
+/*
+ * USE_LIBC_LAST
+ * This implementation wraps the glibc functions with the port as 2nd argument.
+ */
+#if IO_PORT_FUNCTION == USE_LIBC_TARGET_LAST
+void OUTB(uint8_t value, uint16_t port)
+{
+	outb(value, port);
+}
+
+void OUTW(uint16_t value, uint16_t port)
+{
+	outw(value, port);
+}
+
+void OUTL(uint32_t value, uint16_t port)
+{
+	outl(value, port);
+}
+#endif
+
+/*
+ * USE_LIBC_FIRST
+ * This implementation uses libc based functions with the port as first argument
+ * like on BSDs.
+ */
+#if IO_PORT_FUNCTION == USE_LIBC_TARGET_FIRST
+void OUTB(uint8_t value, uint16_t port)
+{
+	outb(port, value);
+}
+
+void OUTW(uint16_t value, uint16_t port)
+{
+	outw(port, value);
+}
+
+void OUTL(uint32_t value, uint16_t port)
+{
+	outl(port, value);
+}
+#endif
+
+/*
+ * LIBC_xxx
+ * INx functions can be shared between _LAST and _FIRST
+ */
+#if IO_PORT_FUNCTION == USE_LIBC_TARGET_LAST || IO_PORT_FUNCTION == USE_LIBC_TARGET_FIRST
+uint8_t INB(uint16_t port)
+{
+	return inb(port);
+}
+
+uint16_t INW(uint16_t port)
+{
+	return inw(port);
+}
+
+uint32_t INL(uint16_t port)
+{
+	return inl(port);
+}
+#endif
+
+/*
+ * USE_DOS
+ * DOS provides the functions under a differnt name.
+ */
+#if IO_PORT_FUNCTION == USE_DOS
+void OUTB(uint8_t value, uint16_t port)
+{
+	outportb(port, value);
+}
+
+void OUTW(uint16_t value, uint16_t port)
+{
+	outportw(port, value);
+}
+
+void OUTL(uint32_t value, uint16_t port)
+{
+	outportl(port, value);
+}
+
+uint8_t INB(uint16_t port)
+{
+	return inportb(port);
+}
+
+uint16_t INW(uint16_t port)
+{
+	return inportw(port);
+}
+
+uint32_t INL(uint16_t port)
+{
+	return inportl(port);
+}
+#endif
+
+/*
+ * USE_ASM
+ * Pure assembly implementation.
+ */
+#if IO_PORT_FUNCTION == USE_ASM
+void OUTB(uint8_t value, uint16_t port)
+{
+	__asm__ volatile ("outb %b0,%w1": :"a" (value), "Nd" (port));
+}
+
+void OUTW(uint16_t value, uint16_t port)
+{
+	__asm__ volatile ("outw %w0,%w1": :"a" (value), "Nd" (port));
+}
+
+void OUTL(uint32_t value, uint16_t port)
+{
+	__asm__ volatile ("outl %0,%w1": :"a" (value), "Nd" (port));
+}
+
+uint8_t INB(uint16_t port)
+{
+	uint8_t value;
+	__asm__ volatile ("inb %w1,%0":"=a" (value):"Nd" (port));
+	return value;
+}
+
+uint16_t INW(uint16_t port)
+{
+	uint16_t value;
+	__asm__ volatile ("inw %w1,%0":"=a" (value):"Nd" (port));
+	return value;
+}
+
+uint32_t INL(uint16_t port)
+{
+	uint32_t value;
+	__asm__ volatile ("inl %1,%0":"=a" (value):"Nd" (port));
+	return value;
+}
+#endif
diff --git a/hwaccess_x86_io.h b/hwaccess_x86_io.h
index 0d16fdd..31d1e86 100644
--- a/hwaccess_x86_io.h
+++ b/hwaccess_x86_io.h
@@ -2,6 +2,8 @@
  * This file is part of the flashrom project.
  *
  * Copyright (C) 2009 Carl-Daniel Hailfinger
+ * Copyright (C) 2022 secunet Security Networks AG
+ * (Written by Thomas Heijligen <thomas.heijligen@secunet.com)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -13,144 +15,23 @@
  * GNU General Public License for more details.
  */
 
+/*
+ * This file contains prototypes for x86 I/O Port access.
+ */
+
 #ifndef __HWACCESS_X86_IO_H__
 #define __HWACCESS_X86_IO_H__ 1
 
-/* sys/io.h provides iopl(2) and x86 I/O port access functions (inb, outb etc).
- * It is included in glibc (thus available also on debian/kFreeBSD) but also in other libcs that mimic glibc,
- * e.g. musl and uclibc. Because we cannot detect the libc or existence of the header or of the instructions
- * themselves safely in here we use some heuristic below:
- * On Android we don't have the header file and no way for I/O port access at all. However, sys/glibc-syscalls.h
- * refers to an iopl implementation and we therefore include at least that one for now. On non-Android we assume
- * that a Linux system's libc has a suitable sys/io.h or (on non-Linux) we depend on glibc to offer it. */
-#if defined(__ANDROID__)
-#include <sys/glibc-syscalls.h>
-#elif defined(__linux__) || defined(__GLIBC__)
-#include <sys/io.h>
-#endif
-
-/* for iopl and outb under Solaris */
-#if defined (__sun)
-#include <sys/sysi86.h>
-#include <sys/psw.h>
-#include <asm/sunddi.h>
-#endif
-
+#include <stdint.h>
+/**
+ */
 int rget_io_perms(void);
 
-/* Clarification about OUTB/OUTW/OUTL argument order:
- * OUT[BWL](val, port)
- */
-
-#if defined(__FreeBSD__) || defined(__DragonFly__)
-  /* Note that Debian/kFreeBSD (FreeBSD kernel with glibc) has conflicting
-   * out[bwl] definitions in machine/cpufunc.h and sys/io.h at least in some
-   * versions. Use machine/cpufunc.h only for plain FreeBSD/DragonFlyBSD.
-   */
-  #include <sys/types.h>
-  #include <machine/cpufunc.h>
-  #define OUTB(x, y) do { u_int outb_tmp = (y); outb(outb_tmp, (x)); } while (0)
-  #define OUTW(x, y) do { u_int outw_tmp = (y); outw(outw_tmp, (x)); } while (0)
-  #define OUTL(x, y) do { u_int outl_tmp = (y); outl(outl_tmp, (x)); } while (0)
-  #define INB(x) __extension__ ({ u_int inb_tmp = (x); inb(inb_tmp); })
-  #define INW(x) __extension__ ({ u_int inw_tmp = (x); inw(inw_tmp); })
-  #define INL(x) __extension__ ({ u_int inl_tmp = (x); inl(inl_tmp); })
-#else
-
-#if defined (__sun)
-  /* Note different order for outb */
-  #define OUTB(x,y) outb(y, x)
-  #define OUTW(x,y) outw(y, x)
-  #define OUTL(x,y) outl(y, x)
-  #define INB  inb
-  #define INW  inw
-  #define INL  inl
-#else
-
-#ifdef __DJGPP__
-
-#include <pc.h>
-
-  #define OUTB(x,y) outportb(y, x)
-  #define OUTW(x,y) outportw(y, x)
-  #define OUTL(x,y) outportl(y, x)
-
-  #define INB  inportb
-  #define INW  inportw
-  #define INL  inportl
-
-#else
-
-#if defined(__MACH__) && defined(__APPLE__)
-    /* Header is part of the DirectHW library. */
-    #include <DirectHW/DirectHW.h>
-#endif
-
-  /* This is the usual glibc interface. */
-  #define OUTB outb
-  #define OUTW outw
-  #define OUTL outl
-  #define INB  inb
-  #define INW  inw
-  #define INL  inl
-#endif
-#endif
-#endif
-
-#if defined(__NetBSD__) || defined (__OpenBSD__)
-  #if defined(__i386__) || defined(__x86_64__)
-    #include <sys/types.h>
-    #include <machine/sysarch.h>
-    #if defined(__NetBSD__)
-      #if defined(__i386__)
-        #define iopl i386_iopl
-      #elif defined(__x86_64__)
-        #define iopl x86_64_iopl
-      #endif
-    #elif defined (__OpenBSD__)
-      #if defined(__i386__)
-        #define iopl i386_iopl
-      #elif defined(__amd64__)
-        #define iopl amd64_iopl
-      #endif
-    #endif
-
-static inline void outb(uint8_t value, uint16_t port)
-{
-	__asm__ volatile ("outb %b0,%w1": :"a" (value), "Nd" (port));
-}
-
-static inline uint8_t inb(uint16_t port)
-{
-	uint8_t value;
-	__asm__ volatile ("inb %w1,%0":"=a" (value):"Nd" (port));
-	return value;
-}
-
-static inline void outw(uint16_t value, uint16_t port)
-{
-	__asm__ volatile ("outw %w0,%w1": :"a" (value), "Nd" (port));
-}
-
-static inline uint16_t inw(uint16_t port)
-{
-	uint16_t value;
-	__asm__ volatile ("inw %w1,%0":"=a" (value):"Nd" (port));
-	return value;
-}
-
-static inline void outl(uint32_t value, uint16_t port)
-{
-	__asm__ volatile ("outl %0,%w1": :"a" (value), "Nd" (port));
-}
-
-static inline uint32_t inl(uint16_t port)
-{
-	uint32_t value;
-	__asm__ volatile ("inl %1,%0":"=a" (value):"Nd" (port));
-	return value;
-}
-  #endif
-#endif
+void OUTB(uint8_t value, uint16_t port);
+void OUTW(uint16_t value, uint16_t port);
+void OUTL(uint32_t value, uint16_t port);
+uint8_t INB(uint16_t port);
+uint16_t INW(uint16_t port);
+uint32_t INL(uint16_t port);
 
 #endif /* __HWACCESS_X86_IO_H__ */
diff --git a/meson.build b/meson.build
index 19b90c5..457823e 100644
--- a/meson.build
+++ b/meson.build
@@ -42,24 +42,6 @@
   add_project_arguments('-DIS_WINDOWS=0', language : 'c')
 endif
 
-if host_machine.system() in ['linux', 'darwin', 'netbsd', 'openbsd']
-  add_project_arguments('-DUSE_IOPL=1', language : 'c')
-else
-  add_project_arguments('-DUSE_IOPL=0', language : 'c')
-endif
-
-if host_machine.system() in ['freebsd', 'dragonfly']
-  add_project_arguments('-DUSE_DEV_IO=1', language : 'c')
-else
-  add_project_arguments('-DUSE_DEV_IO=0', language : 'c')
-endif
-
-if host_machine.system() in ['gnu']
-  add_project_arguments('-DUSE_IOPERM=1', language : 'c')
-else
-  add_project_arguments('-DUSE_IOPERM=0', language : 'c')
-endif
-
 # get defaults from configure
 config_atahpt = get_option('config_atahpt')
 config_atapromise = get_option('config_atapromise')