V4L/DVB (7194): cx88-mpeg: Allow concurrent access to cx88-mpeg devices

It currently isn't possible to open the frontend device of cx88-mpeg devices
(DVB or Blackbird) multiple times concurrently. (for instance, to attach a
signal monitoring tool while reading a stream, or to send a frequency change
ioctl) This patch fixes that condition.
Signed-off-by: Roland Stoll <roland@xindex.de>
Signed-off-by: Ricardo Cerqueira <v4l@cerqueira.org>
Reviewed-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/cx88/cx88-mpeg.c

@@ -609,13 +609,19 @@ static int cx8802_request_acquire(struct cx8802_driver *drv)
 	struct cx88_core *core = drv->core;
 
 	/* Fail a request for hardware if the device is busy. */
-	if (core->active_type_id != CX88_BOARD_NONE)
+	if (core->active_type_id != CX88_BOARD_NONE &&
+	    core->active_type_id != drv->type_id)
 		return -EBUSY;
 
 	if (drv->advise_acquire)
 	{
-		core->active_type_id = drv->type_id;
-		drv->advise_acquire(drv);
+		core->active_ref++;
+		mutex_lock(&drv->core->lock);
+		if (core->active_type_id == CX88_BOARD_NONE) {
+			core->active_type_id = drv->type_id;
+			drv->advise_acquire(drv);
+		}
+		mutex_unlock(&drv->core->lock);
 
 		mpeg_dbg(1,"%s() Post acquire GPIO=%x\n", __FUNCTION__, cx_read(MO_GP0_IO));
 	}
@@ -628,10 +634,12 @@ static int cx8802_request_release(struct cx8802_driver *drv)
 {
 	struct cx88_core *core = drv->core;
 
-	if (drv->advise_release)
+	if (drv->advise_release && --core->active_ref == 0)
 	{
+		mutex_lock(&drv->core->lock);
 		drv->advise_release(drv);
 		core->active_type_id = CX88_BOARD_NONE;
+		mutex_unlock(&drv->core->lock);
 		mpeg_dbg(1,"%s() Post release GPIO=%x\n", __FUNCTION__, cx_read(MO_GP0_IO));
 	}
 

drivers/media/video/cx88/cx88.h

@@ -336,6 +336,7 @@ struct cx88_core {
 	/* cx88-video needs to access cx8802 for hybrid tuner pll access. */
 	struct cx8802_dev          *dvbdev;
 	enum cx88_board_type       active_type_id;
+	int			   active_ref;
 };
 
 struct cx8800_dev;