staging: comedi: (core): add comedi_dev_from_file_info()

Setting `info = comedi_file_info_from_minor(minor)` and `dev =
comedi_dev_from_minor(minor)` in the same function is a bit of a waste.
The latter function is just a call of the former followed by a
conditional return of an embedded pointer (`info->device`) or NULL.  The
former function uses a spin-lock which is where the wastfulness comes
in.

Move the "followed by a conditional return of an embedded pointer" part
into a new function `comedi_dev_from_file_info` and call this instead of
`comedi_dev_from_minor()` in the places where
`comedi_file_info_from_minor()` is also called.

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

drivers/staging/comedi/comedi_fops.c

@@ -103,14 +103,16 @@ static struct comedi_file_info *comedi_file_info_from_minor(unsigned minor)
 	return info;
 }
 
-struct comedi_device *comedi_dev_from_minor(unsigned minor)
+static struct comedi_device *
+comedi_dev_from_file_info(struct comedi_file_info *info)
 {
-	struct comedi_file_info *info;
-
-	info = comedi_file_info_from_minor(minor);
-
 	return info ? info->device : NULL;
 }
+
+struct comedi_device *comedi_dev_from_minor(unsigned minor)
+{
+	return comedi_dev_from_file_info(comedi_file_info_from_minor(minor));
+}
 EXPORT_SYMBOL_GPL(comedi_dev_from_minor);
 
 static struct comedi_subdevice *
@@ -1647,8 +1649,8 @@ static long comedi_unlocked_ioctl(struct file *file, unsigned int cmd,
 				  unsigned long arg)
 {
 	const unsigned minor = iminor(file->f_dentry->d_inode);
-	struct comedi_device *dev = comedi_dev_from_minor(minor);
 	struct comedi_file_info *info = comedi_file_info_from_minor(minor);
+	struct comedi_device *dev = comedi_dev_from_file_info(info);
 	int rc;
 
 	if (!dev)
@@ -1771,7 +1773,7 @@ static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	const unsigned minor = iminor(file->f_dentry->d_inode);
 	struct comedi_file_info *info = comedi_file_info_from_minor(minor);
-	struct comedi_device *dev = comedi_dev_from_minor(minor);
+	struct comedi_device *dev = comedi_dev_from_file_info(info);
 	struct comedi_subdevice *s;
 	struct comedi_async *async;
 	unsigned long start = vma->vm_start;
@@ -1851,7 +1853,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
 	unsigned int mask = 0;
 	const unsigned minor = iminor(file->f_dentry->d_inode);
 	struct comedi_file_info *info = comedi_file_info_from_minor(minor);
-	struct comedi_device *dev = comedi_dev_from_minor(minor);
+	struct comedi_device *dev = comedi_dev_from_file_info(info);
 	struct comedi_subdevice *s;
 
 	if (!dev)
@@ -1897,7 +1899,7 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
 	DECLARE_WAITQUEUE(wait, current);
 	const unsigned minor = iminor(file->f_dentry->d_inode);
 	struct comedi_file_info *info = comedi_file_info_from_minor(minor);
-	struct comedi_device *dev = comedi_dev_from_minor(minor);
+	struct comedi_device *dev = comedi_dev_from_file_info(info);
 
 	if (!dev)
 		return -ENODEV;
@@ -1992,7 +1994,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 	DECLARE_WAITQUEUE(wait, current);
 	const unsigned minor = iminor(file->f_dentry->d_inode);
 	struct comedi_file_info *info = comedi_file_info_from_minor(minor);
-	struct comedi_device *dev = comedi_dev_from_minor(minor);
+	struct comedi_device *dev = comedi_dev_from_file_info(info);
 
 	if (!dev)
 		return -ENODEV;