staging: comedi: don't hijack hardware device private data

comedi_auto_config() associates a Comedi minor device number with an
auto-configured hardware device and comedi_auto_unconfig() disassociates
it.  Currently, these use the hardware device's private data pointer to
point to some allocated storage holding the minor device number.  This
is a bit of a waste of the hardware device's private data pointer,
preventing it from being used for something more useful by the low-level
comedi device drivers.  For example, it would make more sense if
comedi_usb_auto_config() was passed a pointer to the struct
usb_interface instead of the struct usb_device, but this cannot be done
currently because the low-level comedi drivers already use the private
data pointer in the struct usb_interface for something more useful.

This patch stops the comedi core hijacking the hardware device's private
data pointer.  Instead, comedi_auto_config() stores a pointer to the
hardware device's struct device in the struct comedi_device_file_info
associated with the minor device number, and comedi_auto_unconfig()
calls new function comedi_find_board_minor() to recover the minor device
number associated with the hardware device.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedi_fops.c

@@ -2205,6 +2205,7 @@ int comedi_alloc_board_minor(struct device *hardware_device)
 		kfree(info);
 		return -ENOMEM;
 	}
+	info->hardware_device = hardware_device;
 	comedi_device_init(info->device);
 	spin_lock(&comedi_file_info_table_lock);
 	for (i = 0; i < COMEDI_NUM_BOARD_MINORS; ++i) {
@@ -2292,6 +2293,23 @@ void comedi_free_board_minor(unsigned minor)
 	}
 }
 
+int comedi_find_board_minor(struct device *hardware_device)
+{
+	int minor;
+	struct comedi_device_file_info *info;
+
+	for (minor = 0; minor < COMEDI_NUM_BOARD_MINORS; minor++) {
+		spin_lock(&comedi_file_info_table_lock);
+		info = comedi_file_info_table[minor];
+		if (info && info->hardware_device == hardware_device) {
+			spin_unlock(&comedi_file_info_table_lock);
+			return minor;
+		}
+		spin_unlock(&comedi_file_info_table_lock);
+	}
+	return -ENODEV;
+}
+
 int comedi_alloc_subdevice_minor(struct comedi_device *dev,
 				 struct comedi_subdevice *s)
 {

drivers/staging/comedi/comedidev.h

@@ -234,6 +234,7 @@ struct comedi_device_file_info {
 	struct comedi_device *device;
 	struct comedi_subdevice *read_subdevice;
 	struct comedi_subdevice *write_subdevice;
+	struct device *hardware_device;
 };
 
 #ifdef CONFIG_COMEDI_DEBUG

drivers/staging/comedi/drivers.c

@@ -822,25 +822,14 @@ static int comedi_auto_config(struct device *hardware_device,
 	int minor;
 	struct comedi_device_file_info *dev_file_info;
 	int retval;
-	unsigned *private_data = NULL;
 
-	if (!comedi_autoconfig) {
-		dev_set_drvdata(hardware_device, NULL);
+	if (!comedi_autoconfig)
 		return 0;
-	}
 
 	minor = comedi_alloc_board_minor(hardware_device);
 	if (minor < 0)
 		return minor;
 
-	private_data = kmalloc(sizeof(unsigned), GFP_KERNEL);
-	if (private_data == NULL) {
-		retval = -ENOMEM;
-		goto cleanup;
-	}
-	*private_data = minor;
-	dev_set_drvdata(hardware_device, private_data);
-
 	dev_file_info = comedi_get_device_file_info(minor);
 
 	memset(&it, 0, sizeof(it));
@@ -853,25 +842,22 @@ static int comedi_auto_config(struct device *hardware_device,
 	retval = comedi_device_attach(dev_file_info->device, &it);
 	mutex_unlock(&dev_file_info->device->mutex);
 
-cleanup:
-	if (retval < 0) {
-		kfree(private_data);
+	if (retval < 0)
 		comedi_free_board_minor(minor);
-	}
 	return retval;
 }
 
 static void comedi_auto_unconfig(struct device *hardware_device)
 {
-	unsigned *minor = (unsigned *)dev_get_drvdata(hardware_device);
-	if (minor == NULL)
-		return;
-
-	BUG_ON(*minor >= COMEDI_NUM_BOARD_MINORS);
+	int minor;
 
-	comedi_free_board_minor(*minor);
-	dev_set_drvdata(hardware_device, NULL);
-	kfree(minor);
+	if (hardware_device == NULL)
+		return;
+	minor = comedi_find_board_minor(hardware_device);
+	if (minor < 0)
+		return;
+	BUG_ON(minor >= COMEDI_NUM_BOARD_MINORS);
+	comedi_free_board_minor(minor);
 }
 
 int comedi_pci_auto_config(struct pci_dev *pcidev, struct comedi_driver *driver)

drivers/staging/comedi/internal.h

@@ -7,6 +7,7 @@ int insn_inval(struct comedi_device *dev, struct comedi_subdevice *s,
 	       struct comedi_insn *insn, unsigned int *data);
 int comedi_alloc_board_minor(struct device *hardware_device);
 void comedi_free_board_minor(unsigned minor);
+int comedi_find_board_minor(struct device *hardware_device);
 void comedi_reset_async_buf(struct comedi_async *async);
 int comedi_buf_alloc(struct comedi_device *dev, struct comedi_subdevice *s,
 		     unsigned long new_size);