About upstreaming ArmChina NPU driver

[Dejia Shang]

Dear Kernel Maintainers,

I am a driver developer and would like to upstream the ArmChina Zhouyi NPU driver ("Zhouyi" is the brand) to accel subsystem.

The driver is already open sourced (both UMD and KMD) and anyone can find the code from https://github.com/Arm-China/Compass_NPU_Driver.git.

This driver is responsible for scheduling AI inference tasks to the NPU cores (V1/V2/V3). Specifically, a simplified end-to-end flow is:

        1. A TFLite/ONNX model is transformed to an executable binary file in ELF format by the NN graph compiler (designed by ArmChina)
        2. An application loads the executable binary file to UMD and provides the input data.
        3. UMD parses the binary and sends ioctls to KMD (open device, do memory allocation/mmap/free, submit the job descriptor).
        4. KMD dispatches the job to NPU h/w, handles interrupts and updates the execution status.
        5. UMD polls the status of the pre-scheduled job.
        6. The application gets the output results.

So...for the upstreaming,

Q1: do you think our NPU driver is suitable for accel? If the answer is yes, which tree & branch should the patches be based on?

Q2: in thread https://lore.kernel.org/lkml/ec547d33-214f-4952-aa33-c271e9edad63@kernel.org/ showing a similar case, Oded mentioned that:

        "If we would have upstreamed a new driver, the expectation would have been that we would use some drm mechanisms.", and
        "the minimal requirement is to use GEM/BOs for memory management operations".

I guess those requirements are also applicable for the Zhouyi NPU KMD? Currently, the memory management (MM) in KMD is based on dma-mapping APIs, which handles both reserved CMA region(s) and SMMU mapped buffers, and supports the dma-buf framework. Maybe I should replace the implementations with DRM APIs.

Q3: if you have looked at the KMD code, do you think I should make any other major change before submitting the first patch series? Thank you!

Thanks for your time and look forward to your reply~ 😊

Best Regards,
Dejia
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