dvb/bt8xx: kill the big kernel lock

The bt8xx driver only uses the big kernel lock in its dst_ca_ioctl
function and never to serialize against other code, so we can
trivially replace it with a private mutex.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-media@vger.kernel.org
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/dvb/bt8xx/dst_ca.c

@@ -22,7 +22,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/init.h>
-#include <linux/smp_lock.h>
+#include <linux/mutex.h>
 #include <linux/string.h>
 #include <linux/dvb/ca.h>
 #include "dvbdev.h"
@@ -52,6 +52,7 @@
 } while(0)
 
 
+static DEFINE_MUTEX(dst_ca_mutex);
 static unsigned int verbose = 5;
 module_param(verbose, int, 0644);
 MODULE_PARM_DESC(verbose, "verbose startup messages, default is 1 (yes)");
@@ -564,7 +565,7 @@ static long dst_ca_ioctl(struct file *file, unsigned int cmd, unsigned long ioct
 	void __user *arg = (void __user *)ioctl_arg;
 	int result = 0;
 
-	lock_kernel();
+	mutex_lock(&dst_ca_mutex);
 	dvbdev = file->private_data;
 	state = (struct dst_state *)dvbdev->priv;
 	p_ca_message = kmalloc(sizeof (struct ca_msg), GFP_KERNEL);
@@ -652,7 +653,7 @@ static long dst_ca_ioctl(struct file *file, unsigned int cmd, unsigned long ioct
 	kfree (p_ca_slot_info);
 	kfree (p_ca_caps);
 
-	unlock_kernel();
+	mutex_unlock(&dst_ca_mutex);
 	return result;
 }