xref: /OK3568_Linux_fs/external/mpp/doc/design/2.kernel_driver.txt (revision 4882a59341e53eb6f0b4789bf948001014eff981) 
1Hardware kernel driver design (2016.10.17)
2================================================================================
3
4Rockchip has two sets of hardware kernel driver.
5
6The first one is vcodec_service/vpu_service/mpp_service which is a high
7performance stateless frame base hardware kernel driver. This driver supports
8all available codecs that hardware can provide. This driver is used on Android/
9Linux.
10
11Here is the vcodec_service kernel driver framework diagram.
12
13    +-------------+             +-------------+             +-------------+
14    |  client  A  |             |  client  B  |             |  client  C  |
15    +-------------+             +-------------+             +-------------+
16
17userspace
18+------------------------------------------------------------------------------+
19 kernel
20
21    +-------------+             +-------------+             +-------------+
22    |  session A  |             |  session B  |             |  session C  |
23    +-------------+             +-------------+             +-------------+
24    |             |             |             |             |             |
25 waiting         done        waiting         done        waiting         done
26    |             |             |             |             |             |
27+---+---+     +---+---+     +---+---+     +---+---+                   +---+---+
28| task3 |     | task0 |     | task1 |     | task0 |                   | task0 |
29+---+---+     +-------+     +-------+     +-------+                   +---+---+
30    |                                                                     |
31+---+---+                                                             +---+---+
32| task2 |                                                             | task1 |
33+-------+                                                             +-------+
34                                 +-----------+
35                                 |  service  |
36                       +---------+-----------+---------+
37                       |               |               |
38                    waiting         running          done
39                       |               |               |
40                 +-----+-----+   +-----+-----+   +-----+-----+
41                 |  task A2  |   |  task A1  |   |  task C0  |
42                 +-----+-----+   +-----------+   +-----+-----+
43                       |                               |
44                 +-----+-----+                   +-----+-----+
45                 |  task B1  |                   |  task C1  |
46                 +-----+-----+                   +-----+-----+
47                       |                               |
48                 +-----+-----+                   +-----+-----+
49                 |  task A3  |                   |  task A0  |
50                 +-----------+                   +-----+-----+
51                       |
52                 +-----+-----+
53                 |  task B0  |
54                 +-----------+
55
56The principle of this design is to separate user task handling and hardware
57resource management and minimize the kernel serial process time between two
58hardware process operation.
59
60The driver uses session as communication channel. Each userspace client (client)
61will have a kernel session. Client will commit tasks to session. Then hardware
62is managed by service (vpu_service/vcodec_service). Service will provide the
63ability to process tasks in sessions.
64
65When client commits a task to kernel the task will be set to waiting status and
66link to both session waiting list and service waiting list. Then service will
67get task from waiting list to running list and run. When hardware finishs a task
68the task will be moved to done list and put to both service done list and
69session done list. Finally client will get the finished task from session.
70
71