added write functionality

src/io.c

@@ -5,6 +5,8 @@
 #include <linux/gpio.h>
 #include "lcd.h"
 
+static bool advance_ptr(const char* base, ssize_t size, char** ptr);
+
 loff_t lcd_llseek(struct file* filp, loff_t where, int whence)
 {
     return 0;
@@ -17,7 +19,54 @@ ssize_t lcd_read(struct file* filp, char __user* buf, size_t count, loff_t* off)
 
 ssize_t lcd_write(struct file* filp, const char __user* buf, size_t count, loff_t* off)
 {
-    return count;
+    struct lcd_dev* dev = (struct lcd_dev*)filp->private_data;
+    char* kern_buf = NULL;
+    char* cmd_start = NULL;
+    char* cmd_end = NULL;
+    ssize_t retval = 0;
+
+    if(down_interruptible(&dev->sem))
+        return retval;
+
+    kern_buf = (char*)kmalloc(count, GFP_KERNEL);
+    if(kern_buf == NULL)
+    {
+        printk(KERN_ERR "%s: Failed to allocate buffer (%d bytes), aborting write.\n", THIS_MODULE->name, count);
+        retval = -ENOMEM;
+        goto out;
+    }
+
+    if(copy_from_user(kern_buf, buf, count))
+    {
+        printk(KERN_ERR "%s: Failed to copy data from user, aborting write.\n", THIS_MODULE->name);
+        retval = -EFAULT;
+        kfree(kern_buf);
+        goto out;
+    }
+
+    cmd_start = kern_buf;
+    cmd_end = kern_buf;
+
+    while(advance_ptr(kern_buf, count, &cmd_end))
+    {
+        *cmd_end = '\0';
+
+        if(strcmp(cmd_start, "0") == 0)
+            gpio_set_value(dev->gpio, 0);
+        else if(strcmp(cmd_start, "1") == 0)
+            gpio_set_value(dev->gpio, 1);
+        else
+            printk(KERN_WARNING "%s: Unrecognized command \"%s\"\n", THIS_MODULE->name, cmd_start);
+
+        cmd_start = cmd_end + 1;
+    }
+
+    retval = count;
+    kfree(kern_buf);
+
+out:
+    up(&dev->sem);
+    return retval;
 }
 
 long lcd_ioctl(struct file* filp, unsigned int cmd, unsigned long arg)
@@ -31,9 +80,7 @@ int lcd_open(struct inode* inode, struct file* filp)
     dev = container_of(inode->i_cdev, struct lcd_dev, dev);
     filp->private_data = (void*)dev;
 
-    gpio_set_value(dev->gpio, 1);
-
-    printk(KERN_INFO "%s: Opened device\n", THIS_MODULE->name);
+    printk(KERN_DEBUG "%s: Opened device\n", THIS_MODULE->name);
     return 0;
 }
 
@@ -41,9 +88,17 @@ int lcd_release(struct inode* inode, struct file* filp)
 {
     struct lcd_dev* dev;
     dev = (struct lcd_dev*)filp->private_data;
-    gpio_set_value(dev->gpio, 0);
-    printk(KERN_INFO "%s: Released device\n", THIS_MODULE->name);
+    
+    printk(KERN_DEBUG "%s: Released device\n", THIS_MODULE->name);
     return 0;
 }
 
+static bool advance_ptr(const char* base, ssize_t size, char** ptr)
+{
+    while(*ptr - base < size && **ptr != '\n')
+        (*ptr)++;
+
+    return *ptr - base < size;
+}
+
 #endif

src/lcd.c

@@ -10,9 +10,11 @@ MODULE_LICENSE("GPL");
 
 int lcd_major = LCD_MAJOR;
 int lcd_minor = LCD_MINOR;
+int lcd_gpio  = LCD_GPIO;
 
 module_param(lcd_major, int, S_IRUGO);
 module_param(lcd_minor, int, S_IRUGO);
+module_param(lcd_gpio,  int, S_IRUGO);
 
 static struct lcd_dev lcddev = { 0 };
 static int  __init lcd_init_cdev(void);
@@ -60,6 +62,8 @@ static int __init lcd_init_module(void)
         return result;
     }
 
+    sema_init(&lcddev.sem, 1);
+
     result = lcd_init_cdev();
     if(result < 0)
         return result;
@@ -113,5 +117,5 @@ static int  __init lcd_init_gpio(void)
 
 static void __exit lcd_exit_gpio(void)
 {
-    
+
 }

src/lcd.h

@@ -7,13 +7,13 @@
 #define LCD_MAJOR 0
 #define LCD_MINOR 0
 
-extern int lcd_major;
-extern int lcd_minor;
+#define LCD_GPIO 18
 
 struct lcd_dev
 {
     dev_t devno;
     struct cdev dev;
+    struct semaphore sem;
     int gpio;
 };