read now uses semaphores (and still works ;) )

char_dev.c

@@ -55,7 +55,7 @@ static ssize_t device_write(struct file *filp, const char __user *buff, size_t l
 		printk("<1>%s: Device write error!\n",MOD_NAME);
 		return 0;
 	}
-	n_written=0;
+	up(&read_sema);
 	return len;
 }
 

gpio_callbacks.c

@@ -5,8 +5,7 @@ static int get_value(struct gpio_chip *gc, unsigned offset){
 	writeToBuffer(offset);
 	writeToBuffer(CMD_READ);
 
-	n_written=1;
+	down(&read_sema);
-	while(n_written){};
 
 	return pin_status[0];
 }

usb_gpio.c

@@ -2,6 +2,7 @@
 
 static struct gpio_chip ft232_chip;
 static struct subprocess_info *sub_info;
+static struct semaphore read_sema;
 
 static char pin_status[1];
 static int major;
@@ -11,7 +12,6 @@ static uint8_t buff_end;
 
 static uint8_t buffer[BUFFER_SIZE];
 
-static volatile int n_written;
 
 #include "char_dev.c"
 #include "gpio_callbacks.c"
@@ -42,6 +42,8 @@ static int usb_gpio_init(void) {
 	printk("<1>%s: Assigned device major #%d minor #0!\n",MOD_NAME,major);
 	printk("<1>%s: Create device file with: \"mknod /dev/usb_gpio c %d 0\"\n",MOD_NAME,major);
 
+	sema_init(&read_sema,0);
+
 	//GPIO registration
 	ft232_chip.label = MOD_NAME;
 

usb_gpio.h

@@ -12,6 +12,7 @@
 #include <linux/msg.h>
 
 #include <linux/fs.h>
+#include <linux/semaphore.h>
 #include <asm/uaccess.h>
 
 #include "usb_gpio_util.h"