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[RFC/PATCH 0/4] Multi Format Codec 5.0 driver for S5PC110 SoC



Hello,

==============
 Introduction
==============

The purpose of this RFC is to discuss the driver for a hw video codec
embedded in the new Samusng's SoCs. Multi Format Codec 5.0 is able to
handle video decoding of in a range of formats.

So far no hardware codec was supported in V4L2 and this would be the
first one. I guess there are more similar device that would benefit from
a V4L2 unified interface. I suggest a separate control class for codec
devices - V4L2_CTRL_CLASS_CODEC. 

Internally the driver uses videobuf2 framework and CMA memory allocator.
I am aware that those have not yet been merged, but I wanted to start
discussion about the driver earlier so it could be merged sooner. The
driver posted here is the initial version, so I suppose it will require
more work.

==================
 Device interface
==================

In principle the driver bases on the idea of memory-to-memory devices:
it provides a single video node and each opened file handle gets its own
private context with separate buffer queues. Each context consist of 2
buffer queues: OUTPUT (for source buffers, i.e. encoded video frames)
and CAPTURE (for destination buffers, i.e. decoded raw video frames).
The process of decoding video data from stream is a bit more complicated
than typical memory-to-memory processing, that's why the m2m framework
is not directly used (it is too limited for this case). The main reason
for this is the fact that the CAPTURE buffers can be dequeued in a
different order than they queued. The hw block decides which buffer has
been completely processed. This is due to the structure of most
compressed video streams - use of B frames causes that decoding and
display order may be different.

==============================
 Decoding initialization path
==============================

First the OUTPUT queue is initialized. With S_FMT the application
chooses which video format to decode and what size should be the input
buffer. Fourcc values have been defined for different codecs e.g.
V4L2_PIX_FMT_H264 for h264. Then the OUTPUT buffers are requested and
mmaped. The stream header frame is loaded into the first buffer,
queued and streaming is enabled. At this point the hardware is able to
start processing the stream header and afterwards it will have
information about the video dimensions and the size of the buffers with
raw video data.

The next step is setting up the CAPTURE queue and buffers. The width,
height, buffer size and minimum number of buffers can be read with G_FMT
call. The application can request more output buffer if necessary. After
requesting and mmaping buffers the device is ready to decode video
stream.

The stream frames (ES frames) are written to the OUTPUT buffers,
and decoded video frames can be read from the CAPTURE buffers. When no
more source frames are present a single buffer with bytesused set to 0
should be queued. This will inform the driver that processing should be
finished and it can dequeue all video frames that are still left. The
number of such frames is dependent on the stream and its internal
structure (how many frames had to be kept as reference frames for
decoding, etc).

===============
 Usage summary
===============

This is a step by step summary of the video decoding (from user
application point of view, with 2 treads and blocking api):

01. S_FMT(OUTPUT, V4L2_PIX_FMT_H264, ...)
02. REQ_BUFS(OUTPUT, n)
03. for i=1..n MMAP(OUTPUT, i)
04. put stream header to buffer #1
05. QBUF(OUTPUT, #1)
06. STREAM_ON(OUTPUT)
07. G_FMT(CAPTURE)
08. REQ_BUFS(CAPTURE, m)
09. for j=1..m MMAP(CAPTURE, j)
10. for j=1..m QBUF(CAPTURE, #j)
11. STREAM_ON(CAPTURE)

display thread:
12. DQBUF(CAPTURE) -> got decoded video data in buffer #j
13. display buffer #j
14. QBUF(CAPTURE, #j)
15. goto 12

parser thread:
16. put next ES frame to buffer #i
17. QBUF(OUTPUT, #i)
18. DQBUF(OUTPUT) -> get next empty buffer #i
19. goto 16

...

Similar usage sequence can be achieved with single threaded application
and non-blocking api with poll() call.

Branch with MFC, CMA and videobuf2 will be soon available at
http://git.infradead.org/users/kmpark/linux-2.6-samsung/shortlog/refs/heads/mfc
This tree is based on kgene/for-next (Samsung S5P platform 'next' tree).

Please have a look at the code and the idea of how to introduce codec
devices to V4L2. Comments will be very much appreciated.

Best regards,
Kamil Debski

Patch summary:

Kamil Debski (4):
  MFC: Changes in include/linux/videodev2.h for MFC 5.1 codec
  MFC: Add MFC 5.1 driver to plat-s5p
  MFC: Add MFC 5.1 V4L2 driver
  s5pc110: Enable MFC 5.1 on Goni

 arch/arm/mach-s5pv210/Kconfig                |    1 +
 arch/arm/mach-s5pv210/clock.c                |    6 +
 arch/arm/mach-s5pv210/include/mach/map.h     |    4 +
 arch/arm/mach-s5pv210/mach-goni.c            |    1 +
 arch/arm/plat-s5p/Kconfig                    |    5 +
 arch/arm/plat-s5p/Makefile                   |    1 +
 arch/arm/plat-s5p/dev-mfc5.c                 |   37 +
 arch/arm/plat-samsung/include/plat/devs.h    |    2 +
 drivers/media/video/Kconfig                  |    8 +
 drivers/media/video/Makefile                 |    1 +
 drivers/media/video/s5p-mfc/Makefile         |    3 +
 drivers/media/video/s5p-mfc/regs-mfc5.h      |  305 +++++
 drivers/media/video/s5p-mfc/s5p_mfc.c        | 1879 ++++++++++++++++++++++++++
 drivers/media/video/s5p-mfc/s5p_mfc_common.h |  190 +++
 drivers/media/video/s5p-mfc/s5p_mfc_ctrls.h  |  173 +++
 drivers/media/video/s5p-mfc/s5p_mfc_intr.c   |   77 ++
 drivers/media/video/s5p-mfc/s5p_mfc_intr.h   |   26 +
 drivers/media/video/s5p-mfc/s5p_mfc_logmsg.h |   65 +
 drivers/media/video/s5p-mfc/s5p_mfc_memory.h |   32 +
 drivers/media/video/s5p-mfc/s5p_mfc_opr.c    |  800 +++++++++++
 drivers/media/video/s5p-mfc/s5p_mfc_opr.h    |   90 ++
 include/linux/videodev2.h                    |   48 +
 22 files changed, 3754 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/plat-s5p/dev-mfc5.c
 create mode 100644 drivers/media/video/s5p-mfc/Makefile
 create mode 100644 drivers/media/video/s5p-mfc/regs-mfc5.h
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc.c
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_common.h
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_ctrls.h
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_intr.c
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_intr.h
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_logmsg.h
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_memory.h
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_opr.c
 create mode 100644 drivers/media/video/s5p-mfc/s5p_mfc_opr.h

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