Hardware kernel driver design (2016.10.17)
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================================================================================
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Rockchip has two sets of hardware kernel driver.
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The first one is vcodec_service/vpu_service/mpp_service which is a high
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performance stateless frame base hardware kernel driver. This driver supports
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all available codecs that hardware can provide. This driver is used on Android/
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Linux.
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Here is the vcodec_service kernel driver framework diagram.
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+-------------+ +-------------+ +-------------+
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| client A | | client B | | client C |
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+-------------+ +-------------+ +-------------+
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userspace
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+------------------------------------------------------------------------------+
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kernel
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+-------------+ +-------------+ +-------------+
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| session A | | session B | | session C |
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+-------------+ +-------------+ +-------------+
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| | | | | |
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waiting done waiting done waiting done
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| | | | | |
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+---+---+ +---+---+ +---+---+ +---+---+ +---+---+
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| task3 | | task0 | | task1 | | task0 | | task0 |
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+---+---+ +-------+ +-------+ +-------+ +---+---+
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| |
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+---+---+ +---+---+
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| task2 | | task1 |
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+-------+ +-------+
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+-----------+
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| service |
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+---------+-----------+---------+
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| | |
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waiting running done
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| | |
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+-----+-----+ +-----+-----+ +-----+-----+
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| task A2 | | task A1 | | task C0 |
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+-----+-----+ +-----------+ +-----+-----+
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| |
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+-----+-----+ +-----+-----+
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| task B1 | | task C1 |
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+-----+-----+ +-----+-----+
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| |
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+-----+-----+ +-----+-----+
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| task A3 | | task A0 |
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+-----------+ +-----+-----+
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+-----+-----+
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| task B0 |
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+-----------+
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The principle of this design is to separate user task handling and hardware
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resource management and minimize the kernel serial process time between two
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hardware process operation.
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The driver uses session as communication channel. Each userspace client (client)
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will have a kernel session. Client will commit tasks to session. Then hardware
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is managed by service (vpu_service/vcodec_service). Service will provide the
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ability to process tasks in sessions.
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When client commits a task to kernel the task will be set to waiting status and
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link to both session waiting list and service waiting list. Then service will
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get task from waiting list to running list and run. When hardware finishs a task
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the task will be moved to done list and put to both service done list and
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session done list. Finally client will get the finished task from session.
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