1 files changed, 65 insertions, 2 deletions
diff --git a/drivers/media/dvb-core/demux.h b/drivers/media/dvb-core/demux.h
index ccc1f43cb9a9..6d3b95b8939d 100644
--- a/drivers/media/dvb-core/demux.h
+++ b/drivers/media/dvb-core/demux.h
@@ -32,6 +32,49 @@
 #include <linux/time.h>
 #include <linux/dvb/dmx.h>
 
+/**
+ * DOC: Digital TV Demux
+ *
+ * The Kernel Digital TV Demux kABI defines a driver-internal interface for
+ * registering low-level, hardware specific driver to a hardware independent
+ * demux layer. It is only of interest for Digital TV device driver writers.
+ * The header file for this kABI is named demux.h and located in
+ * drivers/media/dvb-core.
+ *
+ * The demux kABI should be implemented for each demux in the system. It is
+ * used to select the TS source of a demux and to manage the demux resources.
+ * When the demux client allocates a resource via the demux kABI, it receives
+ * a pointer to the kABI of that resource.
+ *
+ * Each demux receives its TS input from a DVB front-end or from memory, as
+ * set via this demux kABI. In a system with more than one front-end, the kABI
+ * can be used to select one of the DVB front-ends as a TS source for a demux,
+ * unless this is fixed in the HW platform.
+ *
+ * The demux kABI only controls front-ends regarding to their connections with
+ * demuxes; the kABI used to set the other front-end parameters, such as
+ * tuning, are devined via the Digital TV Frontend kABI.
+ *
+ * The functions that implement the abstract interface demux should be defined
+ * static or module private and registered to the Demux core for external
+ * access. It is not necessary to implement every function in the struct
+ * &dmx_demux. For example, a demux interface might support Section filtering,
+ * but not PES filtering. The kABI client is expected to check the value of any
+ * function pointer before calling the function: the value of NULL means
+ * that the function is not available.
+ *
+ * Whenever the functions of the demux API modify shared data, the
+ * possibilities of lost update and race condition problems should be
+ * addressed, e.g. by protecting parts of code with mutexes.
+ *
+ * Note that functions called from a bottom half context must not sleep.
+ * Even a simple memory allocation without using %GFP_ATOMIC can result in a
+ * kernel thread being put to sleep if swapping is needed. For example, the
+ * Linux Kernel calls the functions of a network device interface from a
+ * bottom half context. Thus, if a demux kABI function is called from network
+ * device code, the function must not sleep.
+ */
+
 /*
  * Common definitions
  */
@@ -187,8 +230,28 @@ struct dmx_section_feed {
 	int (*stop_filtering)(struct dmx_section_feed *feed);
 };
 
-/*
- * Callback functions
+/**
+ * DOC: Demux Callback
+ *
+ * This kernel-space API comprises the callback functions that deliver filtered
+ * data to the demux client. Unlike the other DVB kABIs, these functions are
+ * provided by the client and called from the demux code.
+ *
+ * The function pointers of this abstract interface are not packed into a
+ * structure as in the other demux APIs, because the callback functions are
+ * registered and used independent of each other. As an example, it is possible
+ * for the API client to provide several callback functions for receiving TS
+ * packets and no callbacks for PES packets or sections.
+ *
+ * The functions that implement the callback API need not be re-entrant: when
+ * a demux driver calls one of these functions, the driver is not allowed to
+ * call the function again before the original call returns. If a callback is
+ * triggered by a hardware interrupt, it is recommended to use the Linux
+ * bottom half mechanism or start a tasklet instead of making the callback
+ * function call directly from a hardware interrupt.
+ *
+ * This mechanism is implemented by dmx_ts_cb() and dmx_section_cb()
+ * callbacks.
  */
 
 /**