media: tuner large grain locking

Add a managed token resource that can be created at device level which can be used as a large grain lock by diverse group of drivers such as the media drivers that share a resource.

Media devices often have hardware resources that are shared across several functions. These devices appear as a group of independent devices. Each device implements a function which could be shared by one or more functions supported by the same device. For example, tuner is shared by analog and digital TV functions.

Media drivers that control a single media TV stick are a diversified group. Analog and digital TV function drivers have to coordinate access to their shared functions.

Some media devices provide multiple almost-independent functions. USB and PCI core aids in allowing multiple drivers to handle these almost-independent functions. In this model, a media device could have snd-usb-audio driving the audio function.

As a result, snd-usb-audio driver has to coordinate with the media driver analog and digital function drivers.

A shared managed resource framework at drivers/base level will allow a media device to be controlled by drivers that don't fall under drivers/media and share functions with other media drivers.

Token resource manages a unique named string resource which is derived from common bus_name, and hardware address fields from the struct device.

Interfaces:
devm_token_create()
devm_token_destroy()
devm_token_lock()
devm_token_unlock()
Usage:
Create token: Call devm_token_create() with a token id string. Lock token: Call devm_token_lock() to lock or try lock a token. Unlock token: Call devm_token_unlock().
Destroy token: Call devm_token_destroy() to delete the token.

Signed-off-by Shuah Khan <[email protected]>

---
  drivers/base/Makefile        |    2 +-
  drivers/base/token_devres.c  |  134 ++++++++++++++++++++++++++++++++++++++++++
  include/linux/token_devres.h |   19 ++++++
  3 files changed, 154 insertions(+), 1 deletion(-)

create mode 100644 drivers/base/token_devres.c
create mode 100644 include/linux/token_devres.h

drivers/base/Makefile +1 -1

index 04b314e..924665b 100644
@@ -4,7 +4,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
  			   driver.o class.o platform.o \
  			   cpu.o firmware.o init.o map.o devres.o \
  			   attribute_container.o transport_class.o \
-			   topology.o container.o
+			   topology.o container.o token_devres.o
  obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
  obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
  obj-y			+= power/

drivers/base/token_devres.c new file +0 -0

new file mode 100644
index 0000000..86bcd25

Add a new field tuner_tkn to struct video_device. Drivers can create tuner token using devm_token_create() and initialize the tuner_tkn when frontend is registered with the dvb-core. This change enables drivers to provide a token devres for tuner access control.

Change v4l2-core to lock tuner token for exclusive access to tuner function for analog TV function use. When Tuner token is present, v4l2_open() calls devm_token_lock() to lock the token. If token is busy, -EBUSY is returned to the user-space.

Tuner token is unlocked in error paths in v4l2_open(). This token is held as long as the v4l2 device is open and unlocked from v4l2_release().

Signed-off-by Shuah Khan <[email protected]>

---
  drivers/media/v4l2-core/v4l2-dev.c |   23 ++++++++++++++++++++++-
  include/media/v4l2-dev.h           |    1 +
  2 files changed, 23 insertions(+), 1 deletion(-)

drivers/media/v4l2-core/v4l2-dev.c +1 -0

index 634d863..8dff809 100644
@@ -26,6 +26,7 @@
  #include <linux/kmod.h>
  #include <linux/slab.h>
  #include <asm/uaccess.h>
+#include <linux/token_devres.h>
 
  #include <media/v4l2-common.h>
  #include <media/v4l2-device.h>

@@ -445,6 +446,17 @@ static int v4l2_open(struct inode *inode, struct file *filp)
  		mutex_unlock(&videodev_lock);

drivers/media/v4l2-core/v4l2-dev.c +13 -1

+		dev_info(vdev->dev_parent, "v4l2: Tuner is locked\n");
+	}
+
  	/* and increase the device refcount */
  	video_get(vdev);
  	mutex_unlock(&videodev_lock);

@@ -459,8 +471,13 @@ static int v4l2_open(struct inode *inode, struct file *filp)
  		printk(KERN_DEBUG "%s: open (%d)\n",
  			video_device_node_name(vdev), ret);
  	/* decrease the refcount in case of an error */
-	if (ret)
+	if (ret) {
  		video_put(vdev);
+		if (vdev->tuner_tkn && vdev->dev_parent) {
+			devm_token_unlock(vdev->dev_parent, vdev->tuner_tkn);
+			dev_info(vdev->dev_parent, "v4l2: Tuner is unlocked\n");
+		}
+	}
  	return ret;
  }
 

@@ -479,6 +496,10 @@ static int v4l2_release(struct inode *inode, struct file *filp)
  	/* decrease the refcount unconditionally since the release()
  	   return value is ignored. */
  	video_put(vdev);
+	if (vdev->tuner_tkn && vdev->dev_parent) {
+		devm_token_unlock(vdev->dev_parent, vdev->tuner_tkn);
+		dev_info(vdev->dev_parent, "v4l2: Tuner is unlocked\n");
+	}
  	return ret;
  }
 

include/media/v4l2-dev.h +1 -0

index eec6e46..1676349 100644
@@ -141,6 +141,7 @@ struct video_device
  	/* serialization lock */
  	DECLARE_BITMAP(disable_locking, BASE_VIDIOC_PRIVATE);
  	struct mutex *lock;
+	char *tuner_tkn;
  };
 
  #define media_entity_to_video_device(__e) \

au0828 is changed to use token devres as a large locking for exclusive access to tuner function. A new tuner_tkn field is added to struct au0828_dev. Tuner token is created from au0828 probe() and destroyed from disconnect().

Two new routines au0828_create_token_resources() and au0828_destroy_token_resources() create and destroy the tuner token.

au0828-dvb exports the tuner token to dvb-frontend when it registers the digital frontend using the tuner_tkn field in struct dvb_frontend.

au0828-video exports the tuner token to v4l2-core when it registers the analog function using tuner_tkn field in struct video_device.

Before this change:

- digital tv app disrupts an active analog app when it tries to use the tuner
e.g: tvtime analog video stream stops when kaffeine starts
- analog tv app disrupts another analog app when it tries to use the tuner
e.g: tvtime audio glitches when xawtv starts and vice versa.
- analog tv app disrupts an active digital app when it tries to use the tuner
e.g: kaffeine digital stream stops when tvtime starts
- digital tv app disrupts another digital tv app when it tries to use the tuner
e.g: kaffeine digital stream stops when vlc starts and vice versa

After this change:
- digital tv app detects tuner is busy without disrupting the active app.
- analog tv app detects tuner is busy without disrupting the active analog app.
- analog tv app detects tuner is busy without disrupting the active digital app.
- digital tv app detects tuner is busy without disrupting the active digital app.

Signed-off-by Shuah Khan <[email protected]>

---
  drivers/media/usb/au0828/au0828-core.c  |   42 +++++++++++++++++++++++++++++++
  drivers/media/usb/au0828/au0828-dvb.c   |    1 +
  drivers/media/usb/au0828/au0828-video.c |    4 +++
  drivers/media/usb/au0828/au0828.h       |    4 +++
  4 files changed, 51 insertions(+)

drivers/media/usb/au0828/au0828-core.c +19 -0

index ab45a6f..df04a99 100644
@@ -125,6 +125,37 @@ static int recv_control_msg(struct au0828_dev *dev, u16 request, u32 value,
  	return status;
  }
 
+/* interfaces to create and destroy token resources */
+static int au0828_create_token_resources(struct au0828_dev *dev)
+{
+	int rc = 0, len;
+	char buf[64];
+
+	/* create token devres for tuner */
+	len = snprintf(buf, sizeof(buf),
+		"tuner:%s-%s-%d",
+		dev_name(&dev->usbdev->dev),
+		dev->usbdev->bus->bus_name,
+		dev->board.tuner_addr);
+
+	dev->tuner_tkn = devm_kzalloc(&dev->usbdev->dev, len + 1, GFP_KERNEL);
+	if (!dev->tuner_tkn)
+		return -ENOMEM;
+
+	strcpy(dev->tuner_tkn, buf);
+	rc = devm_token_create(&dev->usbdev->dev, dev->tuner_tkn);

drivers/media/usb/au0828/au0828-core.c +13 -0

+}
+
  static void au0828_usb_release(struct au0828_dev *dev)
  {
  	/* I2C */

@@ -154,6 +185,8 @@ static void au0828_usb_disconnect(struct usb_interface *interface)
  	/* Digital TV */
  	au0828_dvb_unregister(dev);
 
+	au0828_destroy_token_resources(dev);
+
  	usb_set_intfdata(interface, NULL);
  	mutex_lock(&dev->mutex);
  	dev->usbdev = NULL;

@@ -213,6 +246,13 @@ static int au0828_usb_probe(struct usb_interface *interface,
  	dev->usbdev = usbdev;
  	dev->boardnr = id->driver_info;
 
+	/* create token resources */
+	if (au0828_create_token_resources(dev)) {
+		mutex_unlock(&dev->lock);
+		kfree(dev);
+		return -ENOMEM;
+	}
+
  #ifdef CONFIG_VIDEO_AU0828_V4L2
  	dev->v4l2_dev.release = au0828_usb_v4l2_release;
 

@@ -221,6 +261,7 @@ static int au0828_usb_probe(struct usb_interface *interface,
  	if (retval) {
  		pr_err("%s() v4l2_device_register failed\n",
  		       __func__);
+		au0828_destroy_token_resources(dev);
  		mutex_unlock(&dev->lock);
  		kfree(dev);
  		return retval;

@@ -230,6 +271,7 @@ static int au0828_usb_probe(struct usb_interface *interface,
  	if (retval) {
  		pr_err("%s() v4l2_ctrl_handler_init failed\n",
  		       __func__);
+		au0828_destroy_token_resources(dev);
  		mutex_unlock(&dev->lock);
  		kfree(dev);
  		return retval;

drivers/media/usb/au0828/au0828-dvb.c +1 -0

index d8b5d94..1195d29 100755
@@ -412,6 +412,7 @@ static int dvb_register(struct au0828_dev *dev)
  		goto fail_adapter;
  	}
  	dvb->adapter.priv = dev;
+	dvb->frontend->tuner_tkn = dev->tuner_tkn;
 
  	/* register frontend */
  	result = dvb_register_frontend(&dvb->adapter, dvb->frontend);

drivers/media/usb/au0828/au0828-video.c +4 -0

index 385894a..0b50bda 100644
@@ -2018,6 +2018,9 @@ int au0828_analog_register(struct au0828_dev *dev,
  	dev->vdev->lock = &dev->lock;
  	set_bit(V4L2_FL_USE_FH_PRIO, &dev->vdev->flags);
  	strcpy(dev->vdev->name, "au0828a video");
+	/* is there another way v4l2 core can get struct device ?? */
+	dev->vdev->dev_parent = &dev->usbdev->dev;
+	dev->vdev->tuner_tkn = dev->tuner_tkn;
 
  	/* Setup the VBI device */
  	*dev->vbi_dev = au0828_video_template;

@@ -2025,6 +2028,7 @@ int au0828_analog_register(struct au0828_dev *dev,
  	dev->vbi_dev->lock = &dev->lock;
  	set_bit(V4L2_FL_USE_FH_PRIO, &dev->vbi_dev->flags);
  	strcpy(dev->vbi_dev->name, "au0828a vbi");
+	dev->vbi_dev->tuner_tkn = dev->tuner_tkn;
 
  	/* Register the v4l2 device */
  	video_set_drvdata(dev->vdev, dev);

drivers/media/usb/au0828/au0828.h +1 -0

index 7112b9d..11bc933 100644
@@ -23,6 +23,7 @@
  #include <linux/i2c.h>
  #include <linux/i2c-algo-bit.h>
  #include <media/tveeprom.h>
+#include <linux/token_devres.h>
 
  /* Analog */
  #include <linux/videodev2.h>