MFE: Add multi-frontend mutual exclusion

From: Darron Broad <darron@kewl.org>

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.

Priority: normal

Signed-off-by: Darron Broad <darron@kewl.org>

3 files changed, 49 insertions, 1 deletions

diff --git a/linux/drivers/media/dvb/dvb-core/dvb_frontend.c b/linux/drivers/media/dvb/dvb-core/dvb_frontend.c
index 548d90143..46765bc09 100644
--- a/linux/drivers/media/dvb/dvb-core/dvb_frontend.c
+++ b/linux/drivers/media/dvb/dvb-core/dvb_frontend.c
@@ -52,6 +52,7 @@ 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).");
@@ -63,6 +64,8 @@ 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
 
@@ -1820,13 +1823,46 @@ 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)
@@ -1846,6 +1882,8 @@ 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:
@@ -1853,6 +1891,9 @@ 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/linux/drivers/media/dvb/dvb-core/dvbdev.c b/linux/drivers/media/dvb/dvb-core/dvbdev.c
index 0820da504..422af5a0d 100644
--- a/linux/drivers/media/dvb/dvb-core/dvbdev.c
+++ b/linux/drivers/media/dvb/dvb-core/dvbdev.c
@@ -341,6 +341,9 @@ 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/linux/drivers/media/dvb/dvb-core/dvbdev.h b/linux/drivers/media/dvb/dvb-core/dvbdev.h
index 89d12dc47..574e336ba 100644
--- a/linux/drivers/media/dvb/dvb-core/dvbdev.h
+++ b/linux/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 */
 };