V4L/DVB (9227): MFE: Add multi-frontend mutual exclusion

This add frontend R/W mutual exclusion.
Prior to this point in time it was possible to open both
frontends simultaneously which an MFE card cannot support.

In order to stop this, a delayed open is performed which
has the following function:

-  Return EBUSY after a configurable amount of time
   if a frontend is unavailable due to the other being
   in use.

-  Only allow opening of a frontend if the kernel thread
   of the other has stopped.

This solution was chosen to allow switching between
frontends to work as seamlessly as possible. When both
frontends are actually opened simultaneously then one
will only open, but if quick switching is performed
between one of many then the new open will succeed in
a clean fashion rather than interrupting a kernel
thread.

Signed-off-by: Darron Broad <darron@kewl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

3 files changed, 49 insertions, 1 deletions

diff --git a/drivers/media/dvb/dvb-core/dvb_frontend.c b/drivers/media/dvb/dvb-core/dvb_frontend.c
index 26671757c70..62696f86557 100644
--- a/drivers/media/dvb/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb/dvb-core/dvb_frontend.c
@@ -47,6 +47,7 @@ static int dvb_shutdown_timeout;
 static int dvb_force_auto_inversion;
 static int dvb_override_tune_delay;
 static int dvb_powerdown_on_sleep = 1;
+static int dvb_mfe_wait_time = 5;
 
 module_param_named(frontend_debug, dvb_frontend_debug, int, 0644);
 MODULE_PARM_DESC(frontend_debug, "Turn on/off frontend core debugging (default:off).");
@@ -58,6 +59,8 @@ module_param(dvb_override_tune_delay, int, 0644);
 MODULE_PARM_DESC(dvb_override_tune_delay, "0: normal (default), >0 => delay in milliseconds to wait for lock after a tune attempt");
 module_param(dvb_powerdown_on_sleep, int, 0644);
 MODULE_PARM_DESC(dvb_powerdown_on_sleep, "0: do not power down, 1: turn LNB voltage off on sleep (default)");
+module_param(dvb_mfe_wait_time, int, 0644);
+MODULE_PARM_DESC(dvb_mfe_wait_time, "Wait up to <mfe_wait_time> seconds on open() for multi-frontend to become available (default:5 seconds)");
 
 #define dprintk if (dvb_frontend_debug) printk
 
@@ -1706,13 +1709,46 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 	struct dvb_device *dvbdev = file->private_data;
 	struct dvb_frontend *fe = dvbdev->priv;
 	struct dvb_frontend_private *fepriv = fe->frontend_priv;
+	struct dvb_adapter *adapter = fe->dvb;
+	struct dvb_device *mfedev;
+	struct dvb_frontend *mfe;
+	struct dvb_frontend_private *mfepriv;
+	int mferetry;
 	int ret;
 
 	dprintk ("%s\n", __func__);
 
+	if (adapter->mfe_shared) {
+		mutex_lock (&adapter->mfe_lock);
+		if (adapter->mfe_dvbdev != dvbdev) {
+			if (adapter->mfe_dvbdev) {
+				mfedev = adapter->mfe_dvbdev;
+				mfe = mfedev->priv;
+				mfepriv = mfe->frontend_priv;
+				mutex_unlock (&adapter->mfe_lock);
+				mferetry = (dvb_mfe_wait_time << 1);
+				while (mferetry-- && (mfedev->users != -1 || mfepriv->thread != NULL)) {
+					if(msleep_interruptible(500)) {
+						if(signal_pending(current))
+							return -EINTR;
+					}
+				}
+				mutex_lock (&adapter->mfe_lock);
+				mfedev = adapter->mfe_dvbdev;
+				mfe = mfedev->priv;
+				mfepriv = mfe->frontend_priv;
+				if (mfedev->users != -1 || mfepriv->thread != NULL) {
+					ret = -EBUSY;
+					goto err0;
+				}
+			}
+			adapter->mfe_dvbdev = dvbdev;
+		}
+	}
+
 	if (dvbdev->users == -1 && fe->ops.ts_bus_ctrl) {
 		if ((ret = fe->ops.ts_bus_ctrl(fe, 1)) < 0)
-			return ret;
+			goto err0;
 	}
 
 	if ((ret = dvb_generic_open (inode, file)) < 0)
@@ -1732,6 +1768,8 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 		fepriv->events.eventr = fepriv->events.eventw = 0;
 	}
 
+	if (adapter->mfe_shared)
+		mutex_unlock (&adapter->mfe_lock);
 	return ret;
 
 err2:
@@ -1739,6 +1777,9 @@ err2:
 err1:
 	if (dvbdev->users == -1 && fe->ops.ts_bus_ctrl)
 		fe->ops.ts_bus_ctrl(fe, 0);
+err0:
+	if (adapter->mfe_shared)
+		mutex_unlock (&adapter->mfe_lock);
 	return ret;
 }
 
diff --git a/drivers/media/dvb/dvb-core/dvbdev.c b/drivers/media/dvb/dvb-core/dvbdev.c
index 665776d72a4..a113744a56c 100644
--- a/drivers/media/dvb/dvb-core/dvbdev.c
+++ b/drivers/media/dvb/dvb-core/dvbdev.c
@@ -326,6 +326,9 @@ int dvb_register_adapter(struct dvb_adapter *adap, const char *name,
 	adap->name = name;
 	adap->module = module;
 	adap->device = device;
+	adap->mfe_shared = 0;
+	adap->mfe_dvbdev = NULL;
+	mutex_init (&adap->mfe_lock);
 
 	list_add_tail (&adap->list_head, &dvb_adapter_list);
 
diff --git a/drivers/media/dvb/dvb-core/dvbdev.h b/drivers/media/dvb/dvb-core/dvbdev.h
index 89d12dc477a..574e336bac3 100644
--- a/drivers/media/dvb/dvb-core/dvbdev.h
+++ b/drivers/media/dvb/dvb-core/dvbdev.h
@@ -62,6 +62,10 @@ struct dvb_adapter {
 	struct device *device;
 
 	struct module *module;
+
+	int mfe_shared;			/* indicates mutually exclusive frontends */
+	struct dvb_device *mfe_dvbdev;	/* frontend device in use */
+	struct mutex mfe_lock;		/* access lock for thread creation */
 };