From: Ekansh Gupta <[email protected]> Add documentation for the Qualcomm DSP Accelerator (QDA) driver under Documentation/accel/qda/. The documentation covers the driver architecture, GEM-based buffer management, IOMMU context bank isolation, and the RPMsg transport layer.
The user-space API section describes the DRM IOCTLs for session management, GEM buffer allocation, and remote procedure invocation via the FastRPC protocol, along with a typical application lifecycle example. Sections for dynamic debug and basic testing are also included. Wire the new documentation into the Compute Accelerators index at Documentation/accel/index.rst. Assisted-by: Claude:claude-4-6-sonnet Signed-off-by: Ekansh Gupta <[email protected]> --- Documentation/accel/index.rst | 1 + Documentation/accel/qda/index.rst | 13 ++++ Documentation/accel/qda/qda.rst | 146 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 160 insertions(+) diff --git a/Documentation/accel/index.rst b/Documentation/accel/index.rst index cbc7d4c3876a..5901ea7f784c 100644 --- a/Documentation/accel/index.rst +++ b/Documentation/accel/index.rst @@ -10,4 +10,5 @@ Compute Accelerators introduction amdxdna/index qaic/index + qda/index rocket/index diff --git a/Documentation/accel/qda/index.rst b/Documentation/accel/qda/index.rst new file mode 100644 index 000000000000..013400cf9c25 --- /dev/null +++ b/Documentation/accel/qda/index.rst @@ -0,0 +1,13 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +================================== +accel/qda Qualcomm DSP Accelerator +================================== + +The QDA driver provides a DRM accel based interface for Qualcomm DSP offload. +It uses the FastRPC protocol and integrates with DRM and GEM infrastructure +for device and buffer management. + +.. toctree:: + + qda diff --git a/Documentation/accel/qda/qda.rst b/Documentation/accel/qda/qda.rst new file mode 100644 index 000000000000..9f49af6e6acc --- /dev/null +++ b/Documentation/accel/qda/qda.rst @@ -0,0 +1,146 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +===================================== +Qualcomm DSP Accelerator (QDA) Driver +===================================== + +Introduction +============ + +The QDA driver is a DRM accel driver for Qualcomm's DSPs. It provides a +DRM accel based interface for Qualcomm DSP offload, supporting workloads +such as AI inference, computer vision, audio processing, and sensor offload +on Qualcomm SoCs. It uses the FastRPC protocol and integrates with DRM and +GEM infrastructure for device and buffer management. + +Key Features +============ + +* **DRM accel Interface**: Exposes a standard character device node + (e.g., ``/dev/accel/accel0``) via the DRM accel subsystem. +* **FastRPC Protocol**: Implements the FastRPC protocol for communication + between the application processor and the DSP. +* **GEM Buffer Management**: Uses the DRM GEM interface for buffer + allocation, lifecycle management, and DMA-BUF import/export. +* **IOMMU Isolation**: Uses IOMMU context banks to enforce memory isolation + between different DSP user sessions. +* **Modular Design**: Clean separation between the core DRM logic, the + memory manager, and the RPMsg-based transport layer. + +Architecture +============ + +The QDA driver consists of several functional blocks: + +1. **Core Driver (``qda_drv``)**: Manages device registration, file operations, + and DRM accel integration. +2. **Memory Manager (``qda_memory_manager``)**: A flexible memory management + layer that handles IOMMU context banks. It supports pluggable backends + (such as DMA-coherent) to adapt to different SoC memory architectures. +3. **GEM Subsystem**: Implements the DRM GEM interface for buffer management: + + * **``qda_gem``**: Core GEM object management, including allocation, mmap + operations, and buffer lifecycle management. + * **``qda_prime``**: PRIME import functionality for DMA-BUF interoperability + with other kernel subsystems. + +4. **Transport Layer (``qda_rpmsg``)**: Abstraction over the RPMsg framework + to handle low-level message passing with the DSP firmware. +5. **Compute Bus (``qda_compute_bus``)**: A custom virtual bus used to + enumerate and manage the specific compute context banks defined in the + device tree. The bus was introduced because IOMMU context banks (CBs) are + synthetic constructs — not real platform devices — making a platform driver + an incorrect abstraction for them. The earlier platform-driver approach also + had a race condition: device nodes were created before the RPMsg channel + resources were fully initialized, and because ``probe`` runs asynchronously, + applications could open a CB device and attempt to start a session before + the underlying transport was ready. The compute bus makes CB lifetime + explicitly subordinate to the parent QDA device, closing that window. +6. **FastRPC Core (``qda_fastrpc``)**: Implements the protocol logic for + marshalling arguments and handling remote invocations. + +User-Space API +============== + +The driver exposes a set of DRM-compliant IOCTLs: + +* ``DRM_IOCTL_QDA_QUERY``: Query DSP type (e.g., "cdsp", "adsp") + and capabilities. +* ``DRM_IOCTL_QDA_REMOTE_SESSION_CREATE``: Initialize a new process context + on the DSP. +* ``DRM_IOCTL_QDA_REMOTE_INVOKE``: Submit a remote method invocation (the + primary execution unit). +* ``DRM_IOCTL_QDA_GEM_CREATE``: Allocate a GEM buffer object for DSP usage. +* ``DRM_IOCTL_QDA_GEM_MMAP_OFFSET``: Retrieve mmap offsets for memory mapping. +* ``DRM_IOCTL_QDA_REMOTE_MAP`` / ``DRM_IOCTL_QDA_REMOTE_MUNMAP``: Map or unmap + buffers into the DSP's virtual address space. Each accepts a ``request`` + field selecting between a legacy operation (``QDA_MAP_REQUEST_LEGACY`` / + ``QDA_MUNMAP_REQUEST_LEGACY``) and an attribute-based operation + (``QDA_MAP_REQUEST_ATTR`` / ``QDA_MUNMAP_REQUEST_ATTR``). + +Usage Example +============= + +A typical lifecycle for a user-space application: + +1. **Discovery**: Open ``/dev/accel/accel*`` and use + ``DRM_IOCTL_QDA_QUERY`` to identify the DSP domain served by that + device node. +2. **Initialization**: Call ``DRM_IOCTL_QDA_REMOTE_SESSION_CREATE`` to + establish a session and create a process context on the DSP. +3. **Memory**: Allocate buffers via ``DRM_IOCTL_QDA_GEM_CREATE`` or import + DMA-BUFs (PRIME fd) from other drivers using ``DRM_IOCTL_PRIME_FD_TO_HANDLE``. +4. **Execution**: Use ``DRM_IOCTL_QDA_REMOTE_INVOKE`` to pass arguments and + execute functions on the DSP. +5. **Cleanup**: Close file descriptors to automatically release resources and + detach the session. + +Internal Implementation +======================= + +Memory Management +----------------- +The driver's memory manager creates virtual "IOMMU devices" that map to +hardware context banks. This allows the driver to manage multiple isolated +address spaces. The implementation uses a DMA-coherent backend to ensure data consistency +between the CPU and DSP without manual cache maintenance in most cases. + +Debugging +========= +The driver includes extensive dynamic debug support. Enable it via the +kernel's dynamic debug control: + +.. code-block:: bash + + echo "file drivers/accel/qda/* +p" > /sys/kernel/debug/dynamic_debug/control + +Testing +======= +The QDA driver can be exercised using the ``fastrpc_test`` utility from the +FastRPC userspace library. Run the test application: + +.. code-block:: bash + + fastrpc_test -d 3 -U 1 -t linux -a v68 + +**Options** + +``-d domain`` + Select the DSP domain to run on: + + * ``0`` — ADSP + * ``1`` — MDSP + * ``2`` — SDSP + * ``3`` — CDSP *(default on targets with CDSP)* + +``-U unsigned_PD`` + Select signed or unsigned protection domain: + + * ``0`` — signed PD + * ``1`` — unsigned PD *(default)* + +``-t target`` + Target platform: ``android`` or ``linux`` *(default: linux)* + +``-a arch_version`` + DSP architecture version, e.g. ``v68``, ``v75`` *(default: v68)* -- 2.34.1
