This patch adds description for VFIO Mdev support for dfl devices on dfl bus. Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxx> Signed-off-by: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx> --- Documentation/fpga/dfl.rst | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/Documentation/fpga/dfl.rst b/Documentation/fpga/dfl.rst index 0404fe6..f077754 100644 --- a/Documentation/fpga/dfl.rst +++ b/Documentation/fpga/dfl.rst @@ -502,6 +502,26 @@ FME Partial Reconfiguration Sub Feature driver (see drivers/fpga/dfl-fme-pr.c) could be a reference. +VFIO Mdev support for DFL devices +================================= +As we introduced a dfl bus for private features, they could be added to dfl bus +as independent dfl devices. There is a requirement to handle these devices +either by kernel drivers or by direct access from userspace. Usually we bind +the kernel drivers to devices which provide board management functions, and +gives user direct access to devices which cooperate closely with user +controlled Accelerated Function Unit (AFU). We realize this with a VFIO Mdev +implementation. When we bind the vfio-mdev-dfl driver to a dfl device, it +realizes a group of callbacks and registers to the Mdev framework as a +parent (physical) device. It could then create one (available_instances == 1) +mdev device. +Since dfl devices are sub devices of FPGA DFL physical devices (e.g. PCIE +device), which provide no DMA isolation for each sub device, this may leads to +DMA isolation problem if a private feature is designed to be capable of DMA. +The AFU user could potentially access the whole device addressing space and +impact the private feature. So now the general HW design rule is, no DMA +capability for private features. It eliminates the DMA isolation problem. + + Open discussion =============== FME driver exports one ioctl (DFL_FPGA_FME_PORT_PR) for partial reconfiguration -- 2.7.4
