2.3. Digital TV Demux kABI¶

2.3.1. 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 include/media.

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.

2.3.2. Demux Callback API¶

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.

2.3.3. Digital TV Demux device registration functions and data structures¶

enum dmxdev_type: type of demux filter type.

Constants

DMXDEV_TYPE_NONE: no filter set.
DMXDEV_TYPE_SEC: section filter.
DMXDEV_TYPE_PES: Program Elementary Stream (PES) filter.

enum dmxdev_state: state machine for the dmxdev.

Constants

DMXDEV_STATE_FREE: indicates that the filter is freed.
DMXDEV_STATE_ALLOCATED: indicates that the filter was allocated to be used.
DMXDEV_STATE_SET: indicates that the filter parameters are set.
DMXDEV_STATE_GO: indicates that the filter is running.
DMXDEV_STATE_DONE: indicates that a packet was already filtered and the filter is now disabled. Set only if DMX_ONESHOT. See dmx_sct_filter_params.
DMXDEV_STATE_TIMEDOUT: Indicates a timeout condition.

struct dmxdev_feed: digital TV dmxdev feed

Definition

struct dmxdev_feed {
  u16 pid;
  struct dmx_ts_feed *ts;
  struct list_head next;
};

Members

pid: Program ID to be filtered
ts: pointer to struct dmx_ts_feed
next: struct list_head pointing to the next feed.

struct dmxdev_filter: digital TV dmxdev filter

Definition

struct dmxdev_filter {
  union {
    struct dmx_section_filter *sec;
  } filter;
  union {
    struct list_head ts;
    struct dmx_section_feed *sec;
  } feed;
  union {
    struct dmx_sct_filter_params sec;
    struct dmx_pes_filter_params pes;
  } params;
  enum dmxdev_type type;
  enum dmxdev_state state;
  struct dmxdev *dev;
  struct dvb_ringbuffer buffer;
  struct dvb_vb2_ctx vb2_ctx;
  struct mutex mutex;
  struct timer_list timer;
  int todo;
  u8 secheader[3];
};

Members

filter: a union describing a dmxdev filter. Currently used only for section filters.
filter.sec: a struct dmx_section_filter pointer. For section filter only.
feed: a union describing a dmxdev feed. Depending on the filter type, it can be either feed.ts or feed.sec.
feed.ts: a struct list_head list. For TS and PES feeds.
feed.sec: a struct dmx_section_feed pointer. For section feed only.
params: a union describing dmxdev filter parameters. Depending on the filter type, it can be either params.sec or params.pes.
params.sec: a struct dmx_sct_filter_params embedded struct. For section filter only.
params.pes: a struct dmx_pes_filter_params embedded struct. For PES filter only.
type: type of the dmxdev filter, as defined by enum dmxdev_type.
state: state of the dmxdev filter, as defined by enum dmxdev_state.
dev: pointer to struct dmxdev.
buffer: an embedded struct dvb_ringbuffer buffer.
vb2_ctx: control struct for VB2 handler
mutex: protects the access to struct dmxdev_filter.
timer: struct timer_list embedded timer, used to check for feed timeouts. Only for section filter.
todo: index for the secheader. Only for section filter.
secheader: buffer cache to parse the section header. Only for section filter.

struct dmxdev: Describes a digital TV demux device.

Definition

struct dmxdev {
  struct dvb_device *dvbdev;
  struct dvb_device *dvr_dvbdev;
  struct dmxdev_filter *filter;
  struct dmx_demux *demux;
  int filternum;
  int capabilities;
  unsigned int may_do_mmap:1;
  unsigned int exit:1;
#define DMXDEV_CAP_DUPLEX 1;
  struct dmx_frontend *dvr_orig_fe;
  struct dvb_ringbuffer dvr_buffer;
#define DVR_BUFFER_SIZE (10*188*1024);
  struct dvb_vb2_ctx dvr_vb2_ctx;
  struct mutex mutex;
  spinlock_t lock;
};

Members

dvbdev: pointer to struct dvb_device associated with the demux device node.
dvr_dvbdev: pointer to struct dvb_device associated with the dvr device node.
filter: pointer to struct dmxdev_filter.
demux: pointer to struct dmx_demux.
filternum: number of filters.
capabilities: demux capabilities as defined by enum dmx_demux_caps.
may_do_mmap: flag used to indicate if the device may do mmap.
exit: flag to indicate that the demux is being released.
dvr_orig_fe: pointer to struct dmx_frontend.
dvr_buffer: embedded struct dvb_ringbuffer for DVB output.
dvr_vb2_ctx: control struct for VB2 handler
mutex: protects the usage of this structure.
lock: protects access to dmxdev->filter->data.

int dvb_dmxdev_init(struct dmxdev *dmxdev, struct dvb_adapter *adap)¶: initializes a digital TV demux and registers both demux and DVR devices.

Parameters

struct dmxdev * dmxdev: pointer to struct dmxdev.
struct dvb_adapter * adap: pointer to struct dvb_adapter.

void dvb_dmxdev_release(struct dmxdev *dmxdev)¶: releases a digital TV demux and unregisters it.

Parameters

struct dmxdev * dmxdev: pointer to struct dmxdev.

2.3.4. High-level Digital TV demux interface¶

enum dvb_dmx_filter_type: type of demux feed.

Constants

DMX_TYPE_TS: feed is in TS mode.
DMX_TYPE_SEC: feed is in Section mode.

enum dvb_dmx_state: state machine for a demux filter.

Constants

DMX_STATE_FREE: indicates that the filter is freed.
DMX_STATE_ALLOCATED: indicates that the filter was allocated to be used.
DMX_STATE_READY: indicates that the filter is ready to be used.
DMX_STATE_GO: indicates that the filter is running.

struct dvb_demux_filter: Describes a DVB demux section filter.

Definition

struct dvb_demux_filter {
  struct dmx_section_filter filter;
  u8 maskandmode[DMX_MAX_FILTER_SIZE];
  u8 maskandnotmode[DMX_MAX_FILTER_SIZE];
  bool doneq;
  struct dvb_demux_filter *next;
  struct dvb_demux_feed *feed;
  int index;
  enum dvb_dmx_state state;
  enum dvb_dmx_filter_type type;
};

Members

filter: Section filter as defined by struct dmx_section_filter.
maskandmode: logical and bit mask.
maskandnotmode: logical and not bit mask.
doneq: flag that indicates when a filter is ready.
next: pointer to the next section filter.
feed: struct dvb_demux_feed pointer.
index: index of the used demux filter.
state: state of the filter as described by enum dvb_dmx_state.
type: type of the filter as described by enum dvb_dmx_filter_type.

struct dvb_demux_feed: describes a DVB field

Definition

struct dvb_demux_feed {
  union {
    struct dmx_ts_feed ts;
    struct dmx_section_feed sec;
  } feed;
  union {
    dmx_ts_cb ts;
    dmx_section_cb sec;
  } cb;
  struct dvb_demux *demux;
  void *priv;
  enum dvb_dmx_filter_type type;
  enum dvb_dmx_state state;
  u16 pid;
  ktime_t timeout;
  struct dvb_demux_filter *filter;
  u32 buffer_flags;
  enum ts_filter_type ts_type;
  enum dmx_ts_pes pes_type;
  int cc;
  bool pusi_seen;
  u16 peslen;
  struct list_head list_head;
  unsigned int index;
};

Members

feed: a union describing a digital TV feed. Depending on the feed type, it can be either feed.ts or feed.sec.
feed.ts: a struct dmx_ts_feed pointer. For TS feed only.
feed.sec: a struct dmx_section_feed pointer. For section feed only.
cb: a union describing digital TV callbacks. Depending on the feed type, it can be either cb.ts or cb.sec.
cb.ts: a dmx_ts_cb() calback function pointer. For TS feed only.
cb.sec: a dmx_section_cb() callback function pointer. For section feed only.
demux: pointer to struct dvb_demux.
priv: private data that can optionally be used by a DVB driver.
type: type of the filter, as defined by enum dvb_dmx_filter_type.
state: state of the filter as defined by enum dvb_dmx_state.
pid: PID to be filtered.
timeout: feed timeout.
filter: pointer to struct dvb_demux_filter.
buffer_flags: Buffer flags used to report discontinuity users via DVB memory mapped API, as defined by enum dmx_buffer_flags.
ts_type: type of TS, as defined by enum ts_filter_type.
pes_type: type of PES, as defined by enum dmx_ts_pes.
cc: MPEG-TS packet continuity counter
pusi_seen: if true, indicates that a discontinuity was detected. it is used to prevent feeding of garbage from previous section.
peslen: length of the PES (Packet Elementary Stream).
list_head: head for the list of digital TV demux feeds.
index: a unique index for each feed. Can be used as hardware pid filter index.

struct dvb_demux: represents a digital TV demux

Definition

struct dvb_demux {
  struct dmx_demux dmx;
  void *priv;
  int filternum;
  int feednum;
  int (*start_feed)(struct dvb_demux_feed *feed);
  int (*stop_feed)(struct dvb_demux_feed *feed);
  int (*write_to_decoder)(struct dvb_demux_feed *feed, const u8 *buf, size_t len);
  u32 (*check_crc32)(struct dvb_demux_feed *feed, const u8 *buf, size_t len);
  void (*memcopy)(struct dvb_demux_feed *feed, u8 *dst, const u8 *src, size_t len);
  int users;
#define MAX_DVB_DEMUX_USERS 10;
  struct dvb_demux_filter *filter;
  struct dvb_demux_feed *feed;
  struct list_head frontend_list;
  struct dvb_demux_feed *pesfilter[DMX_PES_OTHER];
  u16 pids[DMX_PES_OTHER];
#define DMX_MAX_PID 0x2000;
  struct list_head feed_list;
  u8 tsbuf[204];
  int tsbufp;
  struct mutex mutex;
  spinlock_t lock;
  uint8_t *cnt_storage;
  ktime_t speed_last_time;
  uint32_t speed_pkts_cnt;
};

Members

dmx: embedded struct dmx_demux with demux capabilities and callbacks.
priv: private data that can optionally be used by a DVB driver.
filternum: maximum amount of DVB filters.
feednum: maximum amount of DVB feeds.
start_feed: callback routine to be called in order to start a DVB feed.
stop_feed: callback routine to be called in order to stop a DVB feed.
write_to_decoder: callback routine to be called if the feed is TS and it is routed to an A/V decoder, when a new TS packet is received. Used only on av7110-av.c.
check_crc32: callback routine to check CRC. If not initialized, dvb_demux will use an internal one.
memcopy: callback routine to memcopy received data. If not initialized, dvb_demux will default to memcpy().
users: counter for the number of demux opened file descriptors. Currently, it is limited to 10 users.
filter: pointer to struct dvb_demux_filter.
feed: pointer to struct dvb_demux_feed.
frontend_list: struct list_head with frontends used by the demux.
pesfilter: array of struct dvb_demux_feed with the PES types that will be filtered.
pids: list of filtered program IDs.
feed_list: struct list_head with feeds.
tsbuf: temporary buffer used internally to store TS packets.
tsbufp: temporary buffer index used internally.
mutex: pointer to struct mutex used to protect feed set logic.
lock: pointer to spinlock_t, used to protect buffer handling.
cnt_storage: buffer used for TS/TEI continuity check.
speed_last_time: ktime_t used for TS speed check.
speed_pkts_cnt: packets count used for TS speed check.

int dvb_dmx_init(struct dvb_demux *demux)¶: initialize a digital TV demux struct.

Parameters

struct dvb_demux * demux: struct dvb_demux to be initialized.

Description

Before being able to register a digital TV demux struct, drivers should call this routine. On its typical usage, some fields should be initialized at the driver before calling it.

A typical usecase is:

dvb->demux.dmx.capabilities =
        DMX_TS_FILTERING | DMX_SECTION_FILTERING |
        DMX_MEMORY_BASED_FILTERING;
dvb->demux.priv       = dvb;
dvb->demux.filternum  = 256;
dvb->demux.feednum    = 256;
dvb->demux.start_feed = driver_start_feed;
dvb->demux.stop_feed  = driver_stop_feed;
ret = dvb_dmx_init(&dvb->demux);
if (ret < 0)
        return ret;

void dvb_dmx_release(struct dvb_demux *demux)¶: releases a digital TV demux internal buffers.

Parameters

struct dvb_demux * demux: struct dvb_demux to be released.

Description

The DVB core internally allocates data at demux. This routine releases those data. Please notice that the struct itelf is not released, as it can be embedded on other structs.

void dvb_dmx_swfilter_packets(struct dvb_demux *demux, const u8 *buf, size_t count)¶: use dvb software filter for a buffer with multiple MPEG-TS packets with 188 bytes each.

Parameters

struct dvb_demux * demux: pointer to struct dvb_demux
const u8 * buf: buffer with data to be filtered
size_t count: number of MPEG-TS packets with size of 188.

Description

The routine will discard a DVB packet that don’t start with 0x47.

Use this routine if the DVB demux fills MPEG-TS buffers that are already aligned.

NOTE

The buf size should have size equal to count * 188.

void dvb_dmx_swfilter(struct dvb_demux *demux, const u8 *buf, size_t count)¶: use dvb software filter for a buffer with multiple MPEG-TS packets with 188 bytes each.

Parameters

struct dvb_demux * demux: pointer to struct dvb_demux
const u8 * buf: buffer with data to be filtered
size_t count: number of MPEG-TS packets with size of 188.

Description

If a DVB packet doesn’t start with 0x47, it will seek for the first byte that starts with 0x47.

Use this routine if the DVB demux fill buffers that may not start with a packet start mark (0x47).

NOTE

The buf size should have size equal to count * 188.

void dvb_dmx_swfilter_204(struct dvb_demux *demux, const u8 *buf, size_t count)¶: use dvb software filter for a buffer with multiple MPEG-TS packets with 204 bytes each.

Parameters

struct dvb_demux * demux: pointer to struct dvb_demux
const u8 * buf: buffer with data to be filtered
size_t count: number of MPEG-TS packets with size of 204.

Description

If a DVB packet doesn’t start with 0x47, it will seek for the first byte that starts with 0x47.

Use this routine if the DVB demux fill buffers that may not start with a packet start mark (0x47).

NOTE

The buf size should have size equal to count * 204.

void dvb_dmx_swfilter_raw(struct dvb_demux *demux, const u8 *buf, size_t count)¶: make the raw data available to userspace without filtering

Parameters

struct dvb_demux * demux: pointer to struct dvb_demux
const u8 * buf: buffer with data
size_t count: number of packets to be passed. The actual size of each packet depends on the dvb_demux->feed->cb.ts logic.

Description

Use it if the driver needs to deliver the raw payload to userspace without passing through the kernel demux. That is meant to support some delivery systems that aren’t based on MPEG-TS.

This function relies on dvb_demux->feed->cb.ts to actually handle the buffer.

2.3.5. Driver-internal low-level hardware specific driver demux interface¶

enum ts_filter_type: filter type bitmap for dmx_ts_feed.set()

Constants

TS_PACKET: Send TS packets (188 bytes) to callback (default).
TS_PAYLOAD_ONLY: In case TS_PACKET is set, only send the TS payload (<=184 bytes per packet) to callback
TS_DECODER: Send stream to built-in decoder (if present).
TS_DEMUX: In case TS_PACKET is set, send the TS to the demux device, not to the dvr device

struct dmx_ts_feed: Structure that contains a TS feed filter

Definition

struct dmx_ts_feed {
  int is_filtering;
  struct dmx_demux *parent;
  void *priv;
  int (*set)(struct dmx_ts_feed *feed,u16 pid,int type,enum dmx_ts_pes pes_type, ktime_t timeout);
  int (*start_filtering)(struct dmx_ts_feed *feed);
  int (*stop_filtering)(struct dmx_ts_feed *feed);
};

Members

is_filtering: Set to non-zero when filtering in progress
parent: pointer to struct dmx_demux
priv: pointer to private data of the API client
set: sets the TS filter
start_filtering: starts TS filtering
stop_filtering: stops TS filtering

Description

A TS feed is typically mapped to a hardware PID filter on the demux chip. Using this API, the client can set the filtering properties to start/stop filtering TS packets on a particular TS feed.

struct dmx_section_filter: Structure that describes a section filter

Definition

struct dmx_section_filter {
  u8 filter_value[DMX_MAX_FILTER_SIZE];
  u8 filter_mask[DMX_MAX_FILTER_SIZE];
  u8 filter_mode[DMX_MAX_FILTER_SIZE];
  struct dmx_section_feed *parent;
  void *priv;
};

Members

filter_value: Contains up to 16 bytes (128 bits) of the TS section header that will be matched by the section filter
filter_mask: Contains a 16 bytes (128 bits) filter mask with the bits specified by filter_value that will be used on the filter match logic.
filter_mode: Contains a 16 bytes (128 bits) filter mode.
parent: Back-pointer to struct dmx_section_feed.
priv: Pointer to private data of the API client.

Description

The filter_mask controls which bits of filter_value are compared with the section headers/payload. On a binary value of 1 in filter_mask, the corresponding bits are compared. The filter only accepts sections that are equal to filter_value in all the tested bit positions.

struct dmx_section_feed: Structure that contains a section feed filter

Definition

struct dmx_section_feed {
  int is_filtering;
  struct dmx_demux *parent;
  void *priv;
  int check_crc;
  int (*set)(struct dmx_section_feed *feed,u16 pid, int check_crc);
  int (*allocate_filter)(struct dmx_section_feed *feed, struct dmx_section_filter **filter);
  int (*release_filter)(struct dmx_section_feed *feed, struct dmx_section_filter *filter);
  int (*start_filtering)(struct dmx_section_feed *feed);
  int (*stop_filtering)(struct dmx_section_feed *feed);
};

Members

is_filtering: Set to non-zero when filtering in progress
parent: pointer to struct dmx_demux
priv: pointer to private data of the API client
check_crc: If non-zero, check the CRC values of filtered sections.
set: sets the section filter
allocate_filter: This function is used to allocate a section filter on the demux. It should only be called when no filtering is in progress on this section feed. If a filter cannot be allocated, the function fails with -ENOSPC.
release_filter: This function releases all the resources of a previously allocated section filter. The function should not be called while filtering is in progress on this section feed. After calling this function, the caller should not try to dereference the filter pointer.
start_filtering: starts section filtering
stop_filtering: stops section filtering

Description

A TS feed is typically mapped to a hardware PID filter on the demux chip. Using this API, the client can set the filtering properties to start/stop filtering TS packets on a particular TS feed.

type dmx_ts_cb¶: Typedef: DVB demux TS filter callback function prototype

Syntax

int dmx_ts_cb (const u8 * buffer1, size_t buffer1_length, const u8 * buffer2, size_t buffer2_length, struct dmx_ts_feed * source, u32 * buffer_flags);

Parameters

const u8 * buffer1: Pointer to the start of the filtered TS packets.
size_t buffer1_length: Length of the TS data in buffer1.
const u8 * buffer2: Pointer to the tail of the filtered TS packets, or NULL.
size_t buffer2_length: Length of the TS data in buffer2.
struct dmx_ts_feed * source: Indicates which TS feed is the source of the callback.
u32 * buffer_flags: Address where buffer flags are stored. Those are used to report discontinuity users via DVB memory mapped API, as defined by enum dmx_buffer_flags.

Description

This function callback prototype, provided by the client of the demux API, is called from the demux code. The function is only called when filtering on a TS feed has been enabled using the start_filtering() function at the dmx_demux. Any TS packets that match the filter settings are copied to a circular buffer. The filtered TS packets are delivered to the client using this callback function. It is expected that the buffer1 and buffer2 callback parameters point to addresses within the circular buffer, but other implementations are also possible. Note that the called party should not try to free the memory the buffer1 and buffer2 parameters point to.

When this function is called, the buffer1 parameter typically points to the start of the first undelivered TS packet within a circular buffer. The buffer2 buffer parameter is normally NULL, except when the received TS packets have crossed the last address of the circular buffer and “wrapped” to the beginning of the buffer. In the latter case the buffer1 parameter would contain an address within the circular buffer, while the buffer2 parameter would contain the first address of the circular buffer. The number of bytes delivered with this function (i.e. buffer1_length + buffer2_length) is usually equal to the value of callback_length parameter given in the set() function, with one exception: if a timeout occurs before receiving callback_length bytes of TS data, any undelivered packets are immediately delivered to the client by calling this function. The timeout duration is controlled by the set() function in the TS Feed API.

If a TS packet is received with errors that could not be fixed by the TS-level forward error correction (FEC), the Transport_error_indicator flag of the TS packet header should be set. The TS packet should not be discarded, as the error can possibly be corrected by a higher layer protocol. If the called party is slow in processing the callback, it is possible that the circular buffer eventually fills up. If this happens, the demux driver should discard any TS packets received while the buffer is full and return -EOVERFLOW.

The type of data returned to the callback can be selected by the dmx_ts_feed.**set** function. The type parameter decides if the raw TS packet (TS_PACKET) or just the payload (TS_PACKET|TS_PAYLOAD_ONLY) should be returned. If additionally the TS_DECODER bit is set the stream will also be sent to the hardware MPEG decoder.

Return

0, on success;
-EOVERFLOW, on buffer overflow.

type dmx_section_cb¶: Typedef: DVB demux TS filter callback function prototype

Syntax

int dmx_section_cb (const u8 * buffer1, size_t buffer1_len, const u8 * buffer2, size_t buffer2_len, struct dmx_section_filter * source, u32 * buffer_flags);

Parameters

const u8 * buffer1: Pointer to the start of the filtered section, e.g. within the circular buffer of the demux driver.
size_t buffer1_len: Length of the filtered section data in buffer1, including headers and CRC.
const u8 * buffer2: Pointer to the tail of the filtered section data, or NULL. Useful to handle the wrapping of a circular buffer.
size_t buffer2_len: Length of the filtered section data in buffer2, including headers and CRC.
struct dmx_section_filter * source: Indicates which section feed is the source of the callback.
u32 * buffer_flags: Address where buffer flags are stored. Those are used to report discontinuity users via DVB memory mapped API, as defined by enum dmx_buffer_flags.

Description

This function callback prototype, provided by the client of the demux API, is called from the demux code. The function is only called when filtering of sections has been enabled using the function dmx_ts_feed.**start_filtering**. When the demux driver has received a complete section that matches at least one section filter, the client is notified via this callback function. Normally this function is called for each received section; however, it is also possible to deliver multiple sections with one callback, for example when the system load is high. If an error occurs while receiving a section, this function should be called with the corresponding error type set in the success field, whether or not there is data to deliver. The Section Feed implementation should maintain a circular buffer for received sections. However, this is not necessary if the Section Feed API is implemented as a client of the TS Feed API, because the TS Feed implementation then buffers the received data. The size of the circular buffer can be configured using the dmx_ts_feed.**set** function in the Section Feed API. If there is no room in the circular buffer when a new section is received, the section must be discarded. If this happens, the value of the success parameter should be DMX_OVERRUN_ERROR on the next callback.

enum dmx_frontend_source: Used to identify the type of frontend

Constants

DMX_MEMORY_FE: The source of the demux is memory. It means that the MPEG-TS to be filtered comes from userspace, via write() syscall.
DMX_FRONTEND_0: The source of the demux is a frontend connected to the demux.

struct dmx_frontend: Structure that lists the frontends associated with a demux

Definition

struct dmx_frontend {
  struct list_head connectivity_list;
  enum dmx_frontend_source source;
};

Members

connectivity_list: List of front-ends that can be connected to a particular demux;
source: Type of the frontend.

Description

FIXME: this structure should likely be replaced soon by some: media-controller based logic.

enum dmx_demux_caps: MPEG-2 TS Demux capabilities bitmap

Constants

DMX_TS_FILTERING: set if TS filtering is supported;
DMX_SECTION_FILTERING: set if section filtering is supported;
DMX_MEMORY_BASED_FILTERING: set if write() available.

Description

Those flags are OR’ed in the dmx_demux.capabilities field

DMX_FE_ENTRY ( list): Casts elements in the list of registered front-ends from the generic type struct list_head to the type * struct dmx_frontend

Parameters

list: list of struct dmx_frontend

struct dmx_demux: Structure that contains the demux capabilities and callbacks.

Definition

struct dmx_demux {
  enum dmx_demux_caps capabilities;
  struct dmx_frontend *frontend;
  void *priv;
  int (*open)(struct dmx_demux *demux);
  int (*close)(struct dmx_demux *demux);
  int (*write)(struct dmx_demux *demux, const char __user *buf, size_t count);
  int (*allocate_ts_feed)(struct dmx_demux *demux,struct dmx_ts_feed **feed, dmx_ts_cb callback);
  int (*release_ts_feed)(struct dmx_demux *demux, struct dmx_ts_feed *feed);
  int (*allocate_section_feed)(struct dmx_demux *demux,struct dmx_section_feed **feed, dmx_section_cb callback);
  int (*release_section_feed)(struct dmx_demux *demux, struct dmx_section_feed *feed);
  int (*add_frontend)(struct dmx_demux *demux, struct dmx_frontend *frontend);
  int (*remove_frontend)(struct dmx_demux *demux, struct dmx_frontend *frontend);
  struct list_head *(*get_frontends)(struct dmx_demux *demux);
  int (*connect_frontend)(struct dmx_demux *demux, struct dmx_frontend *frontend);
  int (*disconnect_frontend)(struct dmx_demux *demux);
  int (*get_pes_pids)(struct dmx_demux *demux, u16 *pids);
};

Members

capabilities: Bitfield of capability flags.
frontend: Front-end connected to the demux
priv: Pointer to private data of the API client
open: This function reserves the demux for use by the caller and, if necessary, initializes the demux. When the demux is no longer needed, the function close should be called. It should be possible for multiple clients to access the demux at the same time. Thus, the function implementation should increment the demux usage count when open is called and decrement it when close is called. The demux function parameter contains a pointer to the demux API and instance data. It returns: 0 on success; -EUSERS, if maximum usage count was reached; -EINVAL, on bad parameter.
close: This function reserves the demux for use by the caller and, if necessary, initializes the demux. When the demux is no longer needed, the function close should be called. It should be possible for multiple clients to access the demux at the same time. Thus, the function implementation should increment the demux usage count when open is called and decrement it when close is called. The demux function parameter contains a pointer to the demux API and instance data. It returns: 0 on success; -ENODEV, if demux was not in use (e. g. no users); -EINVAL, on bad parameter.
write: This function provides the demux driver with a memory buffer containing TS packets. Instead of receiving TS packets from the DVB front-end, the demux driver software will read packets from memory. Any clients of this demux with active TS, PES or Section filters will receive filtered data via the Demux callback API (see 0). The function returns when all the data in the buffer has been consumed by the demux. Demux hardware typically cannot read TS from memory. If this is the case, memory-based filtering has to be implemented entirely in software. The demux function parameter contains a pointer to the demux API and instance data. The buf function parameter contains a pointer to the TS data in kernel-space memory. The count function parameter contains the length of the TS data. It returns: 0 on success; -ERESTARTSYS, if mutex lock was interrupted; -EINTR, if a signal handling is pending; -ENODEV, if demux was removed; -EINVAL, on bad parameter.
allocate_ts_feed: Allocates a new TS feed, which is used to filter the TS packets carrying a certain PID. The TS feed normally corresponds to a hardware PID filter on the demux chip. The demux function parameter contains a pointer to the demux API and instance data. The feed function parameter contains a pointer to the TS feed API and instance data. The callback function parameter contains a pointer to the callback function for passing received TS packet. It returns: 0 on success; -ERESTARTSYS, if mutex lock was interrupted; -EBUSY, if no more TS feeds is available; -EINVAL, on bad parameter.
release_ts_feed: Releases the resources allocated with allocate_ts_feed. Any filtering in progress on the TS feed should be stopped before calling this function. The demux function parameter contains a pointer to the demux API and instance data. The feed function parameter contains a pointer to the TS feed API and instance data. It returns: 0 on success; -EINVAL on bad parameter.
allocate_section_feed: Allocates a new section feed, i.e. a demux resource for filtering and receiving sections. On platforms with hardware support for section filtering, a section feed is directly mapped to the demux HW. On other platforms, TS packets are first PID filtered in hardware and a hardware section filter then emulated in software. The caller obtains an API pointer of type dmx_section_feed_t as an out parameter. Using this API the caller can set filtering parameters and start receiving sections. The demux function parameter contains a pointer to the demux API and instance data. The feed function parameter contains a pointer to the TS feed API and instance data. The callback function parameter contains a pointer to the callback function for passing received TS packet. It returns: 0 on success; -EBUSY, if no more TS feeds is available; -EINVAL, on bad parameter.
release_section_feed: Releases the resources allocated with allocate_section_feed, including allocated filters. Any filtering in progress on the section feed should be stopped before calling this function. The demux function parameter contains a pointer to the demux API and instance data. The feed function parameter contains a pointer to the TS feed API and instance data. It returns: 0 on success; -EINVAL, on bad parameter.
add_frontend: Registers a connectivity between a demux and a front-end, i.e., indicates that the demux can be connected via a call to connect_frontend to use the given front-end as a TS source. The client of this function has to allocate dynamic or static memory for the frontend structure and initialize its fields before calling this function. This function is normally called during the driver initialization. The caller must not free the memory of the frontend struct before successfully calling remove_frontend. The demux function parameter contains a pointer to the demux API and instance data. The frontend function parameter contains a pointer to the front-end instance data. It returns: 0 on success; -EINVAL, on bad parameter.
remove_frontend: Indicates that the given front-end, registered by a call to add_frontend, can no longer be connected as a TS source by this demux. The function should be called when a front-end driver or a demux driver is removed from the system. If the front-end is in use, the function fails with the return value of -EBUSY. After successfully calling this function, the caller can free the memory of the frontend struct if it was dynamically allocated before the add_frontend operation. The demux function parameter contains a pointer to the demux API and instance data. The frontend function parameter contains a pointer to the front-end instance data. It returns: 0 on success; -ENODEV, if the front-end was not found, -EINVAL, on bad parameter.
get_frontends: Provides the APIs of the front-ends that have been registered for this demux. Any of the front-ends obtained with this call can be used as a parameter for connect_frontend. The include file demux.h contains the macro DMX_FE_ENTRY() for converting an element of the generic type struct list_head * to the type struct dmx_frontend . The caller must not free the memory of any of the elements obtained via this function call. The **demux* function parameter contains a pointer to the demux API and instance data. It returns a struct list_head pointer to the list of front-end interfaces, or NULL in the case of an empty list.
connect_frontend: Connects the TS output of the front-end to the input of the demux. A demux can only be connected to a front-end registered to the demux with the function add_frontend. It may or may not be possible to connect multiple demuxes to the same front-end, depending on the capabilities of the HW platform. When not used, the front-end should be released by calling disconnect_frontend. The demux function parameter contains a pointer to the demux API and instance data. The frontend function parameter contains a pointer to the front-end instance data. It returns: 0 on success; -EINVAL, on bad parameter.
disconnect_frontend: Disconnects the demux and a front-end previously connected by a connect_frontend call. The demux function parameter contains a pointer to the demux API and instance data. It returns: 0 on success; -EINVAL on bad parameter.
get_pes_pids: Get the PIDs for DMX_PES_AUDIO0, DMX_PES_VIDEO0, DMX_PES_TELETEXT0, DMX_PES_SUBTITLE0 and DMX_PES_PCR0. The demux function parameter contains a pointer to the demux API and instance data. The pids function parameter contains an array with five u16 elements where the PIDs will be stored. It returns: 0 on success; -EINVAL on bad parameter.

2.3. Digital TV Demux kABI¶

2.3.1. Digital TV Demux¶

2.3.2. Demux Callback API¶

2.3.3. Digital TV Demux device registration functions and data structures¶

2.3.4. High-level Digital TV demux interface¶

2.3.5. Driver-internal low-level hardware specific driver demux interface¶

The Linux Kernel

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