176 lines
6.6 KiB
ReStructuredText
176 lines
6.6 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GPL-2.0
|
||
|
|
|
||
|
|
The Virtual Stateless Decoder Driver (visl)
|
||
|
|
===========================================
|
||
|
|
|
||
|
|
A virtual stateless decoder device for stateless uAPI development
|
||
|
|
purposes.
|
||
|
|
|
||
|
|
This tool's objective is to help the development and testing of
|
||
|
|
userspace applications that use the V4L2 stateless API to decode media.
|
||
|
|
|
||
|
|
A userspace implementation can use visl to run a decoding loop even when
|
||
|
|
no hardware is available or when the kernel uAPI for the codec has not
|
||
|
|
been upstreamed yet. This can reveal bugs at an early stage.
|
||
|
|
|
||
|
|
This driver can also trace the contents of the V4L2 controls submitted
|
||
|
|
to it. It can also dump the contents of the vb2 buffers through a
|
||
|
|
debugfs interface. This is in many ways similar to the tracing
|
||
|
|
infrastructure available for other popular encode/decode APIs out there
|
||
|
|
and can help develop a userspace application by using another (working)
|
||
|
|
one as a reference.
|
||
|
|
|
||
|
|
.. note::
|
||
|
|
|
||
|
|
No actual decoding of video frames is performed by visl. The
|
||
|
|
V4L2 test pattern generator is used to write various debug information
|
||
|
|
to the capture buffers instead.
|
||
|
|
|
||
|
|
Module parameters
|
||
|
|
-----------------
|
||
|
|
|
||
|
|
- visl_debug: Activates debug info, printing various debug messages through
|
||
|
|
dprintk. Also controls whether per-frame debug info is shown. Defaults to off.
|
||
|
|
Note that enabling this feature can result in slow performance through serial.
|
||
|
|
|
||
|
|
- visl_transtime_ms: Simulated process time in milliseconds. Slowing down the
|
||
|
|
decoding speed can be useful for debugging.
|
||
|
|
|
||
|
|
- visl_dprintk_frame_start, visl_dprintk_frame_nframes: Dictates a range of
|
||
|
|
frames where dprintk is activated. This only controls the dprintk tracing on a
|
||
|
|
per-frame basis. Note that printing a lot of data can be slow through serial.
|
||
|
|
|
||
|
|
- keep_bitstream_buffers: Controls whether bitstream (i.e. OUTPUT) buffers are
|
||
|
|
kept after a decoding session. Defaults to false so as to reduce the amount of
|
||
|
|
clutter. keep_bitstream_buffers == false works well when live debugging the
|
||
|
|
client program with GDB.
|
||
|
|
|
||
|
|
- bitstream_trace_frame_start, bitstream_trace_nframes: Similar to
|
||
|
|
visl_dprintk_frame_start, visl_dprintk_nframes, but controls the dumping of
|
||
|
|
buffer data through debugfs instead.
|
||
|
|
|
||
|
|
What is the default use case for this driver?
|
||
|
|
---------------------------------------------
|
||
|
|
|
||
|
|
This driver can be used as a way to compare different userspace implementations.
|
||
|
|
This assumes that a working client is run against visl and that the ftrace and
|
||
|
|
OUTPUT buffer data is subsequently used to debug a work-in-progress
|
||
|
|
implementation.
|
||
|
|
|
||
|
|
Information on reference frames, their timestamps, the status of the OUTPUT and
|
||
|
|
CAPTURE queues and more can be read directly from the CAPTURE buffers.
|
||
|
|
|
||
|
|
Supported codecs
|
||
|
|
----------------
|
||
|
|
|
||
|
|
The following codecs are supported:
|
||
|
|
|
||
|
|
- FWHT
|
||
|
|
- MPEG2
|
||
|
|
- VP8
|
||
|
|
- VP9
|
||
|
|
- H.264
|
||
|
|
- HEVC
|
||
|
|
|
||
|
|
visl trace events
|
||
|
|
-----------------
|
||
|
|
The trace events are defined on a per-codec basis, e.g.:
|
||
|
|
|
||
|
|
.. code-block:: bash
|
||
|
|
|
||
|
|
$ ls /sys/kernel/debug/tracing/events/ | grep visl
|
||
|
|
visl_fwht_controls
|
||
|
|
visl_h264_controls
|
||
|
|
visl_hevc_controls
|
||
|
|
visl_mpeg2_controls
|
||
|
|
visl_vp8_controls
|
||
|
|
visl_vp9_controls
|
||
|
|
|
||
|
|
For example, in order to dump HEVC SPS data:
|
||
|
|
|
||
|
|
.. code-block:: bash
|
||
|
|
|
||
|
|
$ echo 1 > /sys/kernel/debug/tracing/events/visl_hevc_controls/v4l2_ctrl_hevc_sps/enable
|
||
|
|
|
||
|
|
The SPS data will be dumped to the trace buffer, i.e.:
|
||
|
|
|
||
|
|
.. code-block:: bash
|
||
|
|
|
||
|
|
$ cat /sys/kernel/debug/tracing/trace
|
||
|
|
video_parameter_set_id 0
|
||
|
|
seq_parameter_set_id 0
|
||
|
|
pic_width_in_luma_samples 1920
|
||
|
|
pic_height_in_luma_samples 1080
|
||
|
|
bit_depth_luma_minus8 0
|
||
|
|
bit_depth_chroma_minus8 0
|
||
|
|
log2_max_pic_order_cnt_lsb_minus4 4
|
||
|
|
sps_max_dec_pic_buffering_minus1 6
|
||
|
|
sps_max_num_reorder_pics 2
|
||
|
|
sps_max_latency_increase_plus1 0
|
||
|
|
log2_min_luma_coding_block_size_minus3 0
|
||
|
|
log2_diff_max_min_luma_coding_block_size 3
|
||
|
|
log2_min_luma_transform_block_size_minus2 0
|
||
|
|
log2_diff_max_min_luma_transform_block_size 3
|
||
|
|
max_transform_hierarchy_depth_inter 2
|
||
|
|
max_transform_hierarchy_depth_intra 2
|
||
|
|
pcm_sample_bit_depth_luma_minus1 0
|
||
|
|
pcm_sample_bit_depth_chroma_minus1 0
|
||
|
|
log2_min_pcm_luma_coding_block_size_minus3 0
|
||
|
|
log2_diff_max_min_pcm_luma_coding_block_size 0
|
||
|
|
num_short_term_ref_pic_sets 0
|
||
|
|
num_long_term_ref_pics_sps 0
|
||
|
|
chroma_format_idc 1
|
||
|
|
sps_max_sub_layers_minus1 0
|
||
|
|
flags AMP_ENABLED|SAMPLE_ADAPTIVE_OFFSET|TEMPORAL_MVP_ENABLED|STRONG_INTRA_SMOOTHING_ENABLED
|
||
|
|
|
||
|
|
|
||
|
|
Dumping OUTPUT buffer data through debugfs
|
||
|
|
------------------------------------------
|
||
|
|
|
||
|
|
If the **VISL_DEBUGFS** Kconfig is enabled, visl will populate
|
||
|
|
**/sys/kernel/debug/visl/bitstream** with OUTPUT buffer data according to the
|
||
|
|
values of bitstream_trace_frame_start and bitstream_trace_nframes. This can
|
||
|
|
highlight errors as broken clients may fail to fill the buffers properly.
|
||
|
|
|
||
|
|
A single file is created for each processed OUTPUT buffer. Its name contains an
|
||
|
|
integer that denotes the buffer sequence, i.e.:
|
||
|
|
|
||
|
|
.. code-block:: c
|
||
|
|
|
||
|
|
snprintf(name, 32, "bitstream%d", run->src->sequence);
|
||
|
|
|
||
|
|
Dumping the values is simply a matter of reading from the file, i.e.:
|
||
|
|
|
||
|
|
For the buffer with sequence == 0:
|
||
|
|
|
||
|
|
.. code-block:: bash
|
||
|
|
|
||
|
|
$ xxd /sys/kernel/debug/visl/bitstream/bitstream0
|
||
|
|
00000000: 2601 af04 d088 bc25 a173 0e41 a4f2 3274 &......%.s.A..2t
|
||
|
|
00000010: c668 cb28 e775 b4ac f53a ba60 f8fd 3aa1 .h.(.u...:.`..:.
|
||
|
|
00000020: 46b4 bcfc 506c e227 2372 e5f5 d7ea 579f F...Pl.'#r....W.
|
||
|
|
00000030: 6371 5eb5 0eb8 23b5 ca6a 5de5 983a 19e4 cq^...#..j]..:..
|
||
|
|
00000040: e8c3 4320 b4ba a226 cbc1 4138 3a12 32d6 ..C ...&..A8:.2.
|
||
|
|
00000050: fef3 247b 3523 4e90 9682 ac8e eb0c a389 ..${5#N.........
|
||
|
|
00000060: ddd0 6cfc 0187 0e20 7aae b15b 1812 3d33 ..l.... z..[..=3
|
||
|
|
00000070: e1c5 f425 a83a 00b7 4f18 8127 3c4c aefb ...%.:..O..'<L..
|
||
|
|
|
||
|
|
For the buffer with sequence == 1:
|
||
|
|
|
||
|
|
.. code-block:: bash
|
||
|
|
|
||
|
|
$ xxd /sys/kernel/debug/visl/bitstream/bitstream1
|
||
|
|
00000000: 0201 d021 49e1 0c40 aa11 1449 14a6 01dc ...!I..@...I....
|
||
|
|
00000010: 7023 889a c8cd 2cd0 13b4 dab0 e8ca 21fe p#....,.......!.
|
||
|
|
00000020: c4c8 ab4c 486e 4e2f b0df 96cc c74e 8dde ...LHnN/.....N..
|
||
|
|
00000030: 8ce7 ee36 d880 4095 4d64 30a0 ff4f 0c5e ...6..@.Md0..O.^
|
||
|
|
00000040: f16b a6a1 d806 ca2a 0ece a673 7bea 1f37 .k.....*...s{..7
|
||
|
|
00000050: 370f 5bb9 1dc4 ba21 6434 bc53 0173 cba0 7.[....!d4.S.s..
|
||
|
|
00000060: dfe6 bc99 01ea b6e0 346b 92b5 c8de 9f5d ........4k.....]
|
||
|
|
00000070: e7cc 3484 1769 fef2 a693 a945 2c8b 31da ..4..i.....E,.1.
|
||
|
|
|
||
|
|
And so on.
|
||
|
|
|
||
|
|
By default, the files are removed during STREAMOFF. This is to reduce the amount
|
||
|
|
of clutter.
|