comedi: ni_mio_common: Conditionally use I/O port or MMIO

In a future patch, the port I/O functions (`inb()`, `outb()`, and
friends will only be declared in the `HAS_IOPORT` configuration option
is enabled.

The "ni_mio_common.c" file contains calls to both port I/O functions and
memory-mapped I/O functions. The file is `#include`d by "ni_atmio.c",
"ni_mio_cs.c", and "ni_pcimio.c" for the ni_atmio, ni_mio_cs, and
ni_pcimio modules, respectively. Only "ni_pcimio.c" defines the
`PCIDMA` macro before including "ni_mio_common.c" and various bits of
code in "ni_mio_common.c" is conditionally compiled according to whether
that macro is defined or not. Currently, the port I/O function calls
are compiled in regardless of whether the `PCIDMA` macro is defined or
not. However, the fact is that the ni_atmio and ni_mio_cs modules will
never call the memory-mapped I/O functions, and the ni_pcimio module
will never call the port I/O functions.

Calls to the port I/O and memory-mapped I/O functions is confined to the
`ni_writel()`, `ni_writew()`, `ni_writeb()`, `ni_readl()`, `ni_readw()`,
and `ni_readb()` functions which do a run-time test to decide whether to
call the port I/O functions or the memory-mapped I/O functions.
Conditionally compile two variants of the functions so they only call
the port I/O functions if the `PCIDMA` macro is undefined (for the
ni_atmio and ni_mio_cs modules), and only call the memory-mapped I/O
functions if the `PCIDMA` macro is defined (for the ni_pcimio module).

Add a run-time check in the `ni_E_init()` function to return an error if
the comedi device has been set up to use port I/O if `PCIDMA` is
defined, or has been set up to use memory-mapped I/O if `PCIDMA` is not
defined.

The changes make it possible to build the ni_pcimio module even if the
port I/O functions have not been declared. (The ni_atmio and ni_mio_cs
modules do still require the port I/O functions to be declared.)

Cc: Arnd Bergmann <[e-mail]>
Cc: Niklas Schnelle <[e-mail]>
Signed-off-by: Ian Abbott <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/comedi/drivers/ni_mio_common.c

···
 #include <linux/comedi/comedi_8255.h>
 #include "mite.h"
 
+#ifdef PCIDMA
+#define IS_PCIMIO 1
+#else
+#define IS_PCIMIO 0
+#endif
+
 /* A timeout count */
 #define NI_TIMEOUT 1000
 
···
 
 static const int num_adc_stages_611x = 3;
 
+#ifdef PCIDMA
+
 static void ni_writel(struct comedi_device *dev, unsigned int data, int reg)
 {
-	if (dev->mmio)
-		writel(data, dev->mmio + reg);
-	else
-		outl(data, dev->iobase + reg);
+	writel(data, dev->mmio + reg);
 }
 
 static void ni_writew(struct comedi_device *dev, unsigned int data, int reg)
 {
-	if (dev->mmio)
-		writew(data, dev->mmio + reg);
-	else
-		outw(data, dev->iobase + reg);
+	writew(data, dev->mmio + reg);
 }
 
 static void ni_writeb(struct comedi_device *dev, unsigned int data, int reg)
 {
-	if (dev->mmio)
-		writeb(data, dev->mmio + reg);
-	else
-		outb(data, dev->iobase + reg);
+	writeb(data, dev->mmio + reg);
 }
 
 static unsigned int ni_readl(struct comedi_device *dev, int reg)
 {
-	if (dev->mmio)
-		return readl(dev->mmio + reg);
+	return readl(dev->mmio + reg);
+}
 
+static unsigned int ni_readw(struct comedi_device *dev, int reg)
+{
+	return readw(dev->mmio + reg);
+}
+
+static unsigned int ni_readb(struct comedi_device *dev, int reg)
+{
+	return readb(dev->mmio + reg);
+}
+
+#else /* PCIDMA */
+
+static void ni_writel(struct comedi_device *dev, unsigned int data, int reg)
+{
+	outl(data, dev->iobase + reg);
+}
+
+static void ni_writew(struct comedi_device *dev, unsigned int data, int reg)
+{
+	outw(data, dev->iobase + reg);
+}
+
+static void ni_writeb(struct comedi_device *dev, unsigned int data, int reg)
+{
+	outb(data, dev->iobase + reg);
+}
+
+static unsigned int ni_readl(struct comedi_device *dev, int reg)
+{
 	return inl(dev->iobase + reg);
 }
 
 static unsigned int ni_readw(struct comedi_device *dev, int reg)
 {
-	if (dev->mmio)
-		return readw(dev->mmio + reg);
-
 	return inw(dev->iobase + reg);
 }
 
 static unsigned int ni_readb(struct comedi_device *dev, int reg)
 {
-	if (dev->mmio)
-		return readb(dev->mmio + reg);
-
 	return inb(dev->iobase + reg);
 }
+
+#endif /* PCIDMA */
 
 /*
  * We automatically take advantage of STC registers that can be
···
 	int i;
 	const char *dev_family = devpriv->is_m_series ? "ni_mseries"
 						      : "ni_eseries";
+	if (!IS_PCIMIO != !dev->mmio) {
+		dev_err(dev->class_dev,
+			"%s: bug! %s device not supported.\n",
+			KBUILD_MODNAME, board->name);
+		return -ENXIO;
+	}
 
 	/* prepare the device for globally-named routes. */
 	if (ni_assign_device_routes(dev_family, board->name,