From 5f2ab1f941fa5a9da6b04f4175a2324dd2a2c70b Mon Sep 17 00:00:00 2001
From: Stefan Krulj <powertomato@gmail.com>
Date: Wed, 11 Jul 2012 00:08:55 +0200
Subject: [PATCH] read now uses semaphores (and still works ;) )

---
 char_dev.c       | 2 +-
 gpio_callbacks.c | 3 +--
 usb_gpio.c       | 4 +++-
 usb_gpio.h       | 1 +
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/char_dev.c b/char_dev.c
index ad57e0d..02a19df 100644
--- a/char_dev.c
+++ b/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;
 }
 
diff --git a/gpio_callbacks.c b/gpio_callbacks.c
index 0043467..3fc5727 100644
--- a/gpio_callbacks.c
+++ b/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;
-	while(n_written){};
+	down(&read_sema);
 
 	return pin_status[0];
 }
diff --git a/usb_gpio.c b/usb_gpio.c
index 33b3cb7..cc95a3f 100644
--- a/usb_gpio.c
+++ b/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;
 
diff --git a/usb_gpio.h b/usb_gpio.h
index 4ba63fc..72188be 100644
--- a/usb_gpio.h
+++ b/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"