Uacce (Unified/User-space-access-intended Accelerator Framework) targets to provide Shared Virtual Addressing (SVA) between accelerators and processes. So accelerator can access any data structure of the main cpu. This differs from the data sharing between cpu and io device, which share data content rather than address. Because of unified address, hardware and user space of process can share the same virtual address in the communication. Uacce is intended to be used with Jean Philippe Brucker's SVA patchset[1], which enables IO side page fault and PASID support. We have keep verifying with Jean's sva/current [2] We also keep verifying with Eric's SMMUv3 Nested Stage patch [3] This series and related zip & qm driver https://github.com/Linaro/linux-kernel-warpdrive/tree/5.4-rc1-uacce-v4 The library and user application: https://github.com/Linaro/warpdrive/tree/wdprd-v1-upstream References: [1] http://jpbrucker.net/sva/ [2] http://www.linux-arm.org/git?p=linux-jpb.git;a=shortlog;h=refs/heads/sva/current [3] https://github.com/eauger/linux/tree/v5.3.0-rc0-2stage-v9 Change History: v4: Based on 5.4-rc1 Considering other driver integrating uacce, if uacce not compiled, uacce_register return error and uacce_unregister is empty. Simplify uacce flag: UACCE_DEV_SVA. Address Greg's comments: Fix state machine, remove potential syslog triggered from user space etc. v3: Recommended by Greg, use sturct uacce_device instead of struct uacce, and use struct *cdev in struct uacce_device, as a result, cdev can be released by itself when refcount decreased to 0. So the two structures are decoupled and self-maintained by themsleves. Also add dev.release for put_device. v2: Address comments from Greg and Jonathan Modify interface uacce_register Drop noiommu mode first v1: 1. Rebase to 5.3-rc1 2. Build on iommu interface 3. Verifying with Jean's sva and Eric's nested mode iommu. 4. User library has developed a lot: support zlib, openssl etc. 5. Move to misc first RFC3: https://lkml.org/lkml/2018/11/12/1951 RFC2: https://lwn.net/Articles/763990/ Background of why Uacce: Von Neumann processor is not good at general data manipulation. It is designed for control-bound rather than data-bound application. The latter need less control path facility and more/specific ALUs. So there are more and more heterogeneous processors, such as encryption/decryption accelerators, TPUs, or EDGE (Explicated Data Graph Execution) processors, introduced to gain better performance or power efficiency for particular applications these days. There are generally two ways to make use of these heterogeneous processors: The first is to make them co-processors, just like FPU. This is good for some application but it has its own cons: It changes the ISA set permanently. You must save all state elements when the process is switched out. But most data-bound processors have a huge set of state elements. It makes the kernel scheduler more complex. The second is Accelerator. It is taken as a IO device from the CPU's point of view (but it need not to be physically). The process, running on CPU, hold a context of the accelerator and send instructions to it as if it calls a function or thread running with FPU. The context is bound with the processor itself. So the state elements remain in the hardware context until the context is released. We believe this is the core feature of an "Accelerator" vs. Co-processor or other heterogeneous processors. The intention of Uacce is to provide the basic facility to backup this scenario. Its first step is to make sure the accelerator and process can share the same address space. So the accelerator ISA can directly address any data structure of the main CPU. This differs from the data sharing between CPU and IO device, which share data content rather than address. So it is different comparing to the other DMA libraries. In the future, we may add more facility to support linking accelerator library to the main application, or managing the accelerator context as special thread. But no matter how, this can be a solid start point for new processor to be used as an "accelerator" as this is the essential requirement. Kenneth Lee (2): uacce: Add documents for uacce uacce: add uacce driver Documentation/ABI/testing/sysfs-driver-uacce | 47 ++ Documentation/misc-devices/uacce.rst | 297 ++++++++ drivers/misc/Kconfig | 1 + drivers/misc/Makefile | 1 + drivers/misc/uacce/Kconfig | 13 + drivers/misc/uacce/Makefile | 2 + drivers/misc/uacce/uacce.c | 1013 ++++++++++++++++++++++++++ include/linux/uacce.h | 167 +++++ include/uapi/misc/uacce.h | 36 + 9 files changed, 1577 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-driver-uacce create mode 100644 Documentation/misc-devices/uacce.rst create mode 100644 drivers/misc/uacce/Kconfig create mode 100644 drivers/misc/uacce/Makefile create mode 100644 drivers/misc/uacce/uacce.c create mode 100644 include/linux/uacce.h create mode 100644 include/uapi/misc/uacce.h -- 2.7.4
