1.20. V4L2 Memory to Memory functions and data structures

struct v4l2_m2m_ops

mem-to-mem device driver callbacks

Definition

struct v4l2_m2m_ops {
  void (*device_run)(void *priv);
  int (*job_ready)(void *priv);
  void (*job_abort)(void *priv);
};

Members

device_run
required. Begin the actual job (transaction) inside this callback. The job does NOT have to end before this callback returns (and it will be the usual case). When the job finishes, v4l2_m2m_job_finish() has to be called.
job_ready
optional. Should return 0 if the driver does not have a job fully prepared to run yet (i.e. it will not be able to finish a transaction without sleeping). If not provided, it will be assumed that one source and one destination buffer are all that is required for the driver to perform one full transaction. This method may not sleep.
job_abort
optional. Informs the driver that it has to abort the currently running transaction as soon as possible (i.e. as soon as it can stop the device safely; e.g. in the next interrupt handler), even if the transaction would not have been finished by then. After the driver performs the necessary steps, it has to call v4l2_m2m_job_finish() (as if the transaction ended normally). This function does not have to (and will usually not) wait until the device enters a state when it can be stopped.
struct v4l2_m2m_queue_ctx

represents a queue for buffers ready to be processed

Definition

struct v4l2_m2m_queue_ctx {
  struct vb2_queue        q;
  struct list_head        rdy_queue;
  spinlock_t rdy_spinlock;
  u8 num_rdy;
  bool buffered;
};

Members

q
pointer to struct vb2_queue
rdy_queue
List of V4L2 mem-to-mem queues
rdy_spinlock
spin lock to protect the struct usage
num_rdy
number of buffers ready to be processed
buffered
is the queue buffered?

Description

Queue for buffers ready to be processed as soon as this instance receives access to the device.

struct v4l2_m2m_ctx

Memory to memory context structure

Definition

struct v4l2_m2m_ctx {
  struct mutex                    *q_lock;
  struct v4l2_m2m_dev             *m2m_dev;
  struct v4l2_m2m_queue_ctx       cap_q_ctx;
  struct v4l2_m2m_queue_ctx       out_q_ctx;
  struct list_head                queue;
  unsigned long                   job_flags;
  wait_queue_head_t finished;
  void *priv;
};

Members

q_lock
struct mutex lock
m2m_dev
opaque pointer to the internal data to handle M2M context
cap_q_ctx
Capture (output to memory) queue context
out_q_ctx
Output (input from memory) queue context
queue
List of memory to memory contexts
job_flags
Job queue flags, used internally by v4l2-mem2mem.c: TRANS_QUEUED, TRANS_RUNNING and TRANS_ABORT.
finished
Wait queue used to signalize when a job queue finished.
priv
Instance private data

Description

The memory to memory context is specific to a file handle, NOT to e.g. a device.

struct v4l2_m2m_buffer

Memory to memory buffer

Definition

struct v4l2_m2m_buffer {
  struct vb2_v4l2_buffer  vb;
  struct list_head        list;
};

Members

vb
pointer to struct vb2_v4l2_buffer
list
list of m2m buffers
void * v4l2_m2m_get_curr_priv(struct v4l2_m2m_dev * m2m_dev)

return driver private data for the currently running instance or NULL if no instance is running

Parameters

struct v4l2_m2m_dev * m2m_dev
opaque pointer to the internal data to handle M2M context
struct vb2_queue * v4l2_m2m_get_vq(struct v4l2_m2m_ctx * m2m_ctx, enum v4l2_buf_type type)

return vb2_queue for the given type

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
enum v4l2_buf_type type
type of the V4L2 buffer, as defined by enum v4l2_buf_type
void v4l2_m2m_try_schedule(struct v4l2_m2m_ctx * m2m_ctx)

check whether an instance is ready to be added to the pending job queue and add it if so.

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx

Description

There are three basic requirements an instance has to meet to be able to run: 1) at least one source buffer has to be queued, 2) at least one destination buffer has to be queued, 3) streaming has to be on.

If a queue is buffered (for example a decoder hardware ringbuffer that has to be drained before doing streamoff), allow scheduling without v4l2 buffers on that queue.

There may also be additional, custom requirements. In such case the driver should supply a custom callback (job_ready in v4l2_m2m_ops) that should return 1 if the instance is ready. An example of the above could be an instance that requires more than one src/dst buffer per transaction.

void v4l2_m2m_job_finish(struct v4l2_m2m_dev * m2m_dev, struct v4l2_m2m_ctx * m2m_ctx)

inform the framework that a job has been finished and have it clean up

Parameters

struct v4l2_m2m_dev * m2m_dev
opaque pointer to the internal data to handle M2M context
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx

Description

Called by a driver to yield back the device after it has finished with it. Should be called as soon as possible after reaching a state which allows other instances to take control of the device.

This function has to be called only after v4l2_m2m_ops->device_run callback has been called on the driver. To prevent recursion, it should not be called directly from the v4l2_m2m_ops->device_run callback though.

int v4l2_m2m_reqbufs(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_requestbuffers * reqbufs)

multi-queue-aware REQBUFS multiplexer

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_requestbuffers * reqbufs
pointer to struct v4l2_requestbuffers
int v4l2_m2m_querybuf(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_buffer * buf)

multi-queue-aware QUERYBUF multiplexer

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_buffer * buf
pointer to struct v4l2_buffer

Description

See v4l2_m2m_mmap() documentation for details.

int v4l2_m2m_qbuf(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_buffer * buf)

enqueue a source or destination buffer, depending on the type

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_buffer * buf
pointer to struct v4l2_buffer
int v4l2_m2m_dqbuf(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_buffer * buf)

dequeue a source or destination buffer, depending on the type

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_buffer * buf
pointer to struct v4l2_buffer
int v4l2_m2m_prepare_buf(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_buffer * buf)

prepare a source or destination buffer, depending on the type

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_buffer * buf
pointer to struct v4l2_buffer
int v4l2_m2m_create_bufs(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_create_buffers * create)

create a source or destination buffer, depending on the type

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_create_buffers * create
pointer to struct v4l2_create_buffers
int v4l2_m2m_expbuf(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct v4l2_exportbuffer * eb)

export a source or destination buffer, depending on the type

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct v4l2_exportbuffer * eb
pointer to struct v4l2_exportbuffer
int v4l2_m2m_streamon(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, enum v4l2_buf_type type)

turn on streaming for a video queue

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
enum v4l2_buf_type type
type of the V4L2 buffer, as defined by enum v4l2_buf_type
int v4l2_m2m_streamoff(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, enum v4l2_buf_type type)

turn off streaming for a video queue

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
enum v4l2_buf_type type
type of the V4L2 buffer, as defined by enum v4l2_buf_type
__poll_t v4l2_m2m_poll(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct poll_table_struct * wait)

poll replacement, for destination buffers only

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct poll_table_struct * wait
pointer to struct poll_table_struct

Description

Call from the driver’s poll() function. Will poll both queues. If a buffer is available to dequeue (with dqbuf) from the source queue, this will indicate that a non-blocking write can be performed, while read will be returned in case of the destination queue.

int v4l2_m2m_mmap(struct file * file, struct v4l2_m2m_ctx * m2m_ctx, struct vm_area_struct * vma)

source and destination queues-aware mmap multiplexer

Parameters

struct file * file
pointer to struct file
struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct vm_area_struct * vma
pointer to struct vm_area_struct

Description

Call from driver’s mmap() function. Will handle mmap() for both queues seamlessly for videobuffer, which will receive normal per-queue offsets and proper videobuf queue pointers. The differentiation is made outside videobuf by adding a predefined offset to buffers from one of the queues and subtracting it before passing it back to videobuf. Only drivers (and thus applications) receive modified offsets.

struct v4l2_m2m_dev * v4l2_m2m_init(const struct v4l2_m2m_ops * m2m_ops)

initialize per-driver m2m data

Parameters

const struct v4l2_m2m_ops * m2m_ops
pointer to struct v4l2_m2m_ops

Description

Usually called from driver’s :c:func:`probe()` function.

Return

returns an opaque pointer to the internal data to handle M2M context

void v4l2_m2m_release(struct v4l2_m2m_dev * m2m_dev)

cleans up and frees a m2m_dev structure

Parameters

struct v4l2_m2m_dev * m2m_dev
opaque pointer to the internal data to handle M2M context

Description

Usually called from driver’s :c:func:`remove()` function.

struct v4l2_m2m_ctx * v4l2_m2m_ctx_init(struct v4l2_m2m_dev * m2m_dev, void * drv_priv, int (*queue_init) (void *priv, struct vb2_queue *src_vq, struct vb2_queue *dst_vq)

allocate and initialize a m2m context

Parameters

struct v4l2_m2m_dev * m2m_dev
opaque pointer to the internal data to handle M2M context
void * drv_priv
driver’s instance private data
int (*)(void *priv, struct vb2_queue *src_vq, struct vb2_queue *dst_vq) queue_init
a callback for queue type-specific initialization function to be used for initializing videobuf_queues

Description

Usually called from driver’s :c:func:`open()` function.

void v4l2_m2m_ctx_release(struct v4l2_m2m_ctx * m2m_ctx)

release m2m context

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx

Description

Usually called from driver’s release() function.

void v4l2_m2m_buf_queue(struct v4l2_m2m_ctx * m2m_ctx, struct vb2_v4l2_buffer * vbuf)

add a buffer to the proper ready buffers list.

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct vb2_v4l2_buffer * vbuf
pointer to struct vb2_v4l2_buffer

Description

Call from videobuf_queue_ops->ops->buf_queue, videobuf_queue_ops callback.

unsigned int v4l2_m2m_num_src_bufs_ready(struct v4l2_m2m_ctx * m2m_ctx)

return the number of source buffers ready for use

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
unsigned int v4l2_m2m_num_dst_bufs_ready(struct v4l2_m2m_ctx * m2m_ctx)

return the number of destination buffers ready for use

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void * v4l2_m2m_next_buf(struct v4l2_m2m_queue_ctx * q_ctx)

return next buffer from the list of ready buffers

Parameters

struct v4l2_m2m_queue_ctx * q_ctx
pointer to struct v4l2_m2m_queue_ctx
void * v4l2_m2m_next_src_buf(struct v4l2_m2m_ctx * m2m_ctx)

return next source buffer from the list of ready buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void * v4l2_m2m_next_dst_buf(struct v4l2_m2m_ctx * m2m_ctx)

return next destination buffer from the list of ready buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void * v4l2_m2m_last_buf(struct v4l2_m2m_queue_ctx * q_ctx)

return last buffer from the list of ready buffers

Parameters

struct v4l2_m2m_queue_ctx * q_ctx
pointer to struct v4l2_m2m_queue_ctx
void * v4l2_m2m_last_src_buf(struct v4l2_m2m_ctx * m2m_ctx)

return last destination buffer from the list of ready buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void * v4l2_m2m_last_dst_buf(struct v4l2_m2m_ctx * m2m_ctx)

return last destination buffer from the list of ready buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
v4l2_m2m_for_each_dst_buf(m2m_ctx, b)

iterate over a list of destination ready buffers

Parameters

m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
b
current buffer of type struct v4l2_m2m_buffer
v4l2_m2m_for_each_src_buf(m2m_ctx, b)

iterate over a list of source ready buffers

Parameters

m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
b
current buffer of type struct v4l2_m2m_buffer
v4l2_m2m_for_each_dst_buf_safe(m2m_ctx, b, n)

iterate over a list of destination ready buffers safely

Parameters

m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
b
current buffer of type struct v4l2_m2m_buffer
n
used as temporary storage
v4l2_m2m_for_each_src_buf_safe(m2m_ctx, b, n)

iterate over a list of source ready buffers safely

Parameters

m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
b
current buffer of type struct v4l2_m2m_buffer
n
used as temporary storage
struct vb2_queue * v4l2_m2m_get_src_vq(struct v4l2_m2m_ctx * m2m_ctx)

return vb2_queue for source buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct vb2_queue * v4l2_m2m_get_dst_vq(struct v4l2_m2m_ctx * m2m_ctx)

return vb2_queue for destination buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void * v4l2_m2m_buf_remove(struct v4l2_m2m_queue_ctx * q_ctx)

take off a buffer from the list of ready buffers and return it

Parameters

struct v4l2_m2m_queue_ctx * q_ctx
pointer to struct v4l2_m2m_queue_ctx
void * v4l2_m2m_src_buf_remove(struct v4l2_m2m_ctx * m2m_ctx)

take off a source buffer from the list of ready buffers and return it

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void * v4l2_m2m_dst_buf_remove(struct v4l2_m2m_ctx * m2m_ctx)

take off a destination buffer from the list of ready buffers and return it

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
void v4l2_m2m_buf_remove_by_buf(struct v4l2_m2m_queue_ctx * q_ctx, struct vb2_v4l2_buffer * vbuf)

take off exact buffer from the list of ready buffers

Parameters

struct v4l2_m2m_queue_ctx * q_ctx
pointer to struct v4l2_m2m_queue_ctx
struct vb2_v4l2_buffer * vbuf
the buffer to be removed
void v4l2_m2m_src_buf_remove_by_buf(struct v4l2_m2m_ctx * m2m_ctx, struct vb2_v4l2_buffer * vbuf)

take off exact source buffer from the list of ready buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct vb2_v4l2_buffer * vbuf
the buffer to be removed
void v4l2_m2m_dst_buf_remove_by_buf(struct v4l2_m2m_ctx * m2m_ctx, struct vb2_v4l2_buffer * vbuf)

take off exact destination buffer from the list of ready buffers

Parameters

struct v4l2_m2m_ctx * m2m_ctx
m2m context assigned to the instance given by struct v4l2_m2m_ctx
struct vb2_v4l2_buffer * vbuf
the buffer to be removed
void v4l2_m2m_buf_copy_metadata(const struct vb2_v4l2_buffer * out_vb, struct vb2_v4l2_buffer * cap_vb, bool copy_frame_flags)

copy buffer metadata from the output buffer to the capture buffer

Parameters

const struct vb2_v4l2_buffer * out_vb
the output buffer that is the source of the metadata.
struct vb2_v4l2_buffer * cap_vb
the capture buffer that will receive the metadata.
bool copy_frame_flags
copy the KEY/B/PFRAME flags as well.

Description

This helper function copies the timestamp, timecode (if the TIMECODE buffer flag was set), field and the TIMECODE, KEYFRAME, BFRAME, PFRAME and TSTAMP_SRC_MASK flags from out_vb to cap_vb.

If copy_frame_flags is false, then the KEYFRAME, BFRAME and PFRAME flags are not copied. This is typically needed for encoders that set this bits explicitly.