staging: comedi: drivers: introduce comedi_request_region()

Introduce a helper function to handle the request_region() for legacy
comedi drivers.

As pointed out by Ian Abbott, legacy devices are configured manually
with the "comedi_config" program. The error messages are useful
diagnostics when trying to attach to these boards.

Providing a helper function allows consolidating the error messages
in the drivers and providing a consistent format for the errors.

This helper also sets the dev->iobase automatically for the driver
if the request_region() is successful.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedidev.h

@@ -348,6 +348,9 @@ void comedi_buf_memcpy_from(struct comedi_async *async, unsigned int offset,
 
 int comedi_alloc_subdevices(struct comedi_device *, int);
 
+int comedi_request_region(struct comedi_device *,
+			  unsigned long start, unsigned long len);
+
 int comedi_auto_config(struct device *, struct comedi_driver *,
 		       unsigned long context);
 void comedi_auto_unconfig(struct device *);

drivers/staging/comedi/drivers.c

@@ -337,6 +337,33 @@ static void comedi_report_boards(struct comedi_driver *driv)
 		pr_info(" %s\n", driv->driver_name);
 }
 
+/**
+ * comedi_request_region() - Request an I/O reqion for a legacy driver.
+ * @dev: comedi_device struct
+ * @start: base address of the I/O reqion
+ * @len: length of the I/O region
+ */
+int comedi_request_region(struct comedi_device *dev,
+			  unsigned long start, unsigned long len)
+{
+	if (!start) {
+		dev_warn(dev->class_dev,
+			 "%s: a I/O base address must be specified\n",
+			 dev->board_name);
+		return -EINVAL;
+	}
+
+	if (!request_region(start, len, dev->board_name)) {
+		dev_warn(dev->class_dev, "%s: I/O port conflict (%#lx,%lu)\n",
+			 dev->board_name, start, len);
+		return -EIO;
+	}
+	dev->iobase = start;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(comedi_request_region);
+
 int comedi_device_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 {
 	struct comedi_driver *driv;