Hi Kenneth, On 10/08/18 04:39, Kenneth Lee wrote: >> You can achieve everything you want to achieve with existing upstream >> solution. Re-inventing a whole new driver infrastructure should really >> be motivated with strong and obvious reasons. > > I want to understand better of your idea. If I create some unified helper > APIs in drivers/iommu/, say: > > wd_create_dev(parent_dev, wd_dev) > wd_release_dev(wd_dev) > > The API create chrdev to take request from user space for open(resource > allocation), iomap, epoll (irq), and dma_map(with pasid automatically). > > Do you think it is acceptable? Maybe not drivers/iommu/ :) That subsystem only contains tools for dealing with DMA, I don't think epoll, resource enumeration or iomap fit in there. Creating new helpers seems to be precisely what we're trying to avoid in this thread, and vfio-mdev does provide the components that you describe, so I wouldn't discard it right away. When the GPU, net, block or another subsystem doesn't fit your needs, either because your accelerator provides some specialized function, or because for performance reasons your client wants direct MMIO access, you can at least build your driver and library on top of those existing VFIO components: * open allocates a partition of an accelerator. * vfio_device_info, vfio_region_info and vfio_irq_info enumerates available resources. * vfio_irq_set deals with epoll. * mmap gives you a private MMIO doorbell. * vfio_iommu_type1 provides the DMA operations. Currently missing: * Sharing the parent IOMMU between mdev, which is also what the "IOMMU aware mediated device" series tackles, and seems like a logical addition to VFIO. I'd argue that the existing IOMMU ops (or ones implemented by the SVA series) can be used to deal with this * The interface to discover an accelerator near your memory node, or one that you can chain with other devices. If I understood correctly the conclusion was that the API (a topology description in sysfs?) should be common to various subsystems, in which case vfio-mdev (or the mediating driver) could also use it. * The queue abstraction discussed on patch 3/7. Perhaps the current vfio resource description of MMIO and IRQ is sufficient here as well, since vendors tend to each implement their own queue schemes. If you need additional features, read/write fops give the mediating driver a lot of freedom. To support features that are too specific for drivers/vfio/ you can implement a config space with capabilities and registers of your choice. If you're versioning the capabilities, the code to handle them could even be shared between different accelerator drivers and libraries. Thanks, Jean
