Let's have some direct-access I/O methods as well.

src/drivers/device/cdev.cpp

@@ -111,21 +111,21 @@ CDev::~CDev()
 int
 CDev::init()
 {
-	int ret = OK;
-
 	// base class init first
-	ret = Device::init();
+	int ret = Device::init();
 
 	if (ret != OK)
 		goto out;
 
 	// now register the driver
-	ret = register_driver(_devname, &fops, 0666, (void *)this);
+	if (_devname != nullptr) {
+		ret = register_driver(_devname, &fops, 0666, (void *)this);
 
-	if (ret != OK)
+		if (ret != OK)
-		goto out;
+			goto out;
 
-	_registered = true;
+		_registered = true;
+	}
 
 out:
 	return ret;
@@ -395,4 +395,25 @@ cdev_poll(struct file *filp, struct pollfd *fds, bool setup)
 	return cdev->poll(filp, fds, setup);
 }
 
+int
+CDev::read(unsigned offset, void *data, unsigned count)
+{
+	errno = ENODEV;
+	return -1;
+}
+
+int
+CDev::write(unsigned offset, void *data, unsigned count)
+{
+	errno = ENODEV;
+	return -1;
+}
+
+int
+CDev::ioctl(unsigned operation, unsigned &arg)
+{
+	errno = ENODEV;
+	return -1;
+}
+
 } // namespace device

src/drivers/device/device.h

@@ -85,7 +85,7 @@ protected:
 	 */
 	Device(const char *name,
 	       int irq = 0);
-	~Device();
+	virtual ~Device();
 
 	/**
 	 * Initialise the driver and make it ready for use.
@@ -189,7 +189,7 @@ public:
 	/**
 	 * Destructor
 	 */
-	~CDev();
+	virtual ~CDev();
 
 	virtual int	init();
 
@@ -287,6 +287,43 @@ public:
 	 */
 	bool            is_open() { return _open_count > 0; }
 
+	/*
+	 * Direct access methods.
+	 */
+
+	/**
+	 * Read directly from the device.
+	 *
+	 * The actual size of each unit quantity is device-specific.
+	 *
+	 * @param offset	The device offset at which to start reading
+	 * @param data		The buffer into which the read values should be placed.
+	 * @param count		The number of items to read, defaults to 1.
+	 * @return		count on success, < 0 on error.
+	 */
+	virtual int	read(unsigned offset, void *data, unsigned count = 1);
+
+	/**
+	 * Write directly to the device.
+	 *
+	 * The actual size of each unit quantity is device-specific.
+	 *
+	 * @param address	The device address at which to start writing.
+	 * @param data		The buffer from which values should be read.
+	 * @param count		The number of registers to write, defaults to 1.
+	 * @return		count on success, < 0 on error.
+	 */	 
+	virtual int	write(unsigned address, void *data, unsigned count = 1);
+
+	/**
+	 * Perform a device-specific operation.
+	 *
+	 * @param operation	The operation to perform
+	 * @param arg		An argument to the operation.
+	 * @return		< 0 on error
+	 */
+	virtual int	ioctl(unsigned operation, unsigned &arg);
+
 protected:
 	/**
 	 * Pointer to the default cdev file operations table; useful for
@@ -396,9 +433,9 @@ public:
 	    const char *devname,
 	    uint32_t base,
 	    int irq = 0);
-	~PIO();
+	virtual ~PIO();
 
-	int		init();
+	virtual int	init();
 
 protected:
 
@@ -407,7 +444,7 @@ protected:
 	 *
 	 * @param offset	Register offset in bytes from the base address.
 	 */
-	uint32_t reg(uint32_t offset) {
+	uint32_t	reg(uint32_t offset) {
 		return *(volatile uint32_t *)(_base + offset);
 	}