Some small improvements to GPIO driver

TODO

@@ -938,6 +938,7 @@ o Network (net/, drivers/net)
                  TM4C         YES                     YES
                eZ80           NO                      NO
                LPC17xx        YES                     YES (not tested)
+               LPC43xx        YES                     YES (not tested)
                DMxxx NIC      NO                      NO
                PIC32          NO                      NO
                RGMP           ???                     ???
@@ -1602,7 +1603,7 @@ o Build system
   Priority:    Low.
 
   Title:       NATIVE WINDOWS BUILD BROKEN
-  Description: The way that apps/ no generates Kmenu files depends on changes added
+  Description: The way that apps/ now generates Kmenu files depends on changes added
                to apps/tools/mkkconfig.sh.  Similar changes need to be made to
                apps/tools/mkkconfig.bat to restore the Windows Native build.
                UPDATE: The mkkconfig.bat script has been updated and appears to work.

drivers/ioexpander/gpio.c

@@ -86,7 +86,7 @@ static const struct file_operations g_gpio_output_ops =
 {
   gpio_open,  /* open */
   gpio_close, /* close */
-  NULL,       /* read */
+  gpio_read,  /* read */
   gpio_write, /* write */
   NULL,       /* seek */
   gpio_ioctl  /* ioctl */

include/nuttx/ioexpander/gpio.h

@@ -78,19 +78,33 @@ struct gpio_common_dev_s
 
 struct gpio_input_dev_s
 {
+  /* Common fields */
+
   bool gpin_output;
   uint8_t gpin_unused[3];
+
+  /* Fields unique to input pins */
+
   CODE int (*gpin_read)(FAR struct gpio_input_dev_s *dev);
+
+  /* Lower-half private definitions may follow */
 };
 
 /* The interface to a GPIO input pin */
 
 struct gpio_output_dev_s
 {
+  /* Common fields */
+
   bool gpout_output;
   uint8_t gpout_unused[3];
+
+  /* Fields unique to output pins */
+
   CODE int (*gpout_read)(FAR struct gpio_output_dev_s *dev);
   CODE int (*gpout_write)(FAR struct gpio_output_dev_s *dev, int value);
+
+  /* Lower-half private definitions may follow */
 };
 
 /****************************************************************************