The kernel offers a wide variety of interfaces to support the development of device drivers. Altera offers a host of pci express pcie reference designs and application notes. The linux uio drivers at drivers uio in the kernel tree do not provide any facilities for the usermode side to set up dma buffers. Interrupt driven user space application with the uio driver. Userspace driver cannot have interrupt handlers implemented they have to poll for interrupt.
Binding nic drivers as dpdk uses its own pollmode drivers in userspace instead of traditional kernel drivers, the kernel needs to be told to use a different, passthrough style driver for the devices. This document is an only somewhat organized collection of some of those interfaces it will hopefully get better over time. Devices needing only memory mapped io access do not require a kernel driver. Vfio is a better choice if iommu is available, but often. To support pci style interrupts a minimal kernel module using the linux uio framework is required. One potential option could be to use the uio interface see also this blog. Handling gpio interrupts in userspace on linux with uio. In addition, scattergather mode works with problems, that i heard. These reference designs and application notes offer readymade solutions that can leveraged for feasibility studies, device selections, and design proofing on altera fpgas and socs. Add dma capabilities to linux uio driver c programming. At rst, i introduce the device driver environment dde, followed by a brief overview of pci and the linux uio driver framework. The apis are detailed in the kernel usb programming guide kerneldoc, from the source code. Quick and easy device drivers for embedded linux using uio 12,402 views.
Unfortunately, the current linux dma infrastructure doesnt have a sane way to expose these capabilities. User space driver can directly mmap devmem memory to their virtual address space and need no context switching. Feb 25, 2020 udmabuf is a linux device driver that allocates contiguous memory blocks in the kernel space as dma buffers and makes them available from the user space. You might not even have to write the kernel space driver if you use the linux uio driver framework. I want to transfer data from ps to pl through dma driver running on arm corei. The driver needs some kernel space code to link the physical device to the userspace component of the driver see figure 1. A new user level driver framework for linux virtual function io originally developed by tom lyon cisco iommubased dma and interrupt isolation full devices access mmio, io port, pci config efficient interrupt mechanisms modular iommu and device backends not limited to sriov. Eventually, when you have exhausted all the previous user space options, you will find yourself having to write a device driver to access a piece of hardware attached to your device. Transfer data from ps to pl through dma using linux device. The userspace io howto the linux kernel documentation. One possible advantage of this is that i might get access to dma and therefore speed things up quite a bit. If its a driver for a pci device, it should register itself as a pci driver in the usual.
The framework is a character mode kernel driver in driversuio which runs as a layer under a. In particular, being able to access memory made available through the dma mapping api, may be particularly useful. This device can also be used to block for interrupts. Mar 12, 2017 quick and easy device drivers for embedded linux using uio. But im still missing one last thing, its probably easy, but im new to embedded linux. Initialize the device through the mmapped memory regions. The userspace driver each uio driver represented by device node devuiox x 0 for. We report on our implementation, discuss problems related to dma. The dma memory allocator uses hugepages to allocate physically contiguous dmasafe memory.
This page is intended to give more details on the xilinx drivers for linux, such as testing, how to use the drivers, known issues, etc. Chris simmonds, i am a professional trainer, author and consultant in embedded linux and embedded android. Its now possible to use a complex peripheral with interrupts and dma under linux using uio and the genericuio driver rather than having to. A new user level driver framework for linux virtual function io originally developed by tom lyon cisco iommubased dma and interrupt isolation full devices access mmio, io port, pci config efficient interrupt mechanisms modular iommu and device backends. Dear experts i need help regarding interrupt handling using uio. Intended audience this document is fully intended to be viewed and reference by morethanipnine ways customers. The existing hardware supports up to 2 dma windows, one is 479 2gb long, uses 4k pages and called default 32bit window. A poll mode driver pmd consists of apis, provided through the bsd driver running in user space, to configure the devices and their respective queues. Each driver provides attributes that are used to read or write variables. Oct 10, 2014 the linux kernel provides a userspace io subsystem uio which enables some types of drivers to be written almost entirely in userspace see basic documentation here. Uio provides the infrastructure so you can just readselectepoll on a file to wait on. Userspace driver future uio is a good start uio primarily needs support for dma to enable a broader range of drivers driver specific memory allocation and region characteristic info plan is to convert this driver to a uio driver with dma helper extensions some thought still required on how to properly abstract these extensions. An overview over related work will conclude this chapter.
This function copies a buffer of bytes from userspace to the kernel space. In particular, being able to access memory made available through the dmamapping api, may be particularly useful. I am new to linux device drivers, this might be a trivial question for some of you. This driver allows using pci device with message signalled interrupt from userspace. I made the following vivado project attached as image. It is intended that these memory blocks are used as dma buffers when a user application implements device driver in user space using uio user space io. So your best bet is to ensure you never pass a highmem buffer into a usb driver. Linux device drivers are typically designed as kernel drivers running in kernel space. The linux kernel provides a userspace io subsystem uio which enables some types of drivers to be written almost entirely in userspace see basic documentation here.
Zedboard forums is currently readonly while it under goes maintenance. Nov 14, 2018 a zerocopy linux driver and a userspace interface library for xilinxs axi dma and vdma ip blocks. This is done by via a character device that the user program can open, memory map, and perform io operations with. I would like to present here a simple solution to write an interrupt driven user space application with the help of the generic user io kernel driver. Eventually, when you have exhausted all the previous user space options, you will find yourself having to write a device driver to. The uio framework defines a small kernelspace component that performs two key tasks.
I have previously been building the linux kernel using the. These serve as bridges for communication between the processing system and fpga programmable logic fabric, through one of the dma ports on the zynq processing system. Vfio is a better choice if iommu is available, but often userspace. If its a driver for a pci device, it should register itself as. The linux driver implementers api guide the linux kernel 4. This command is used to dma the data from host to card. The drivers included in the kernel tree are intended to run on arm zynq. Userspace driver cannot perform dma as dma capable memory can be allocated from kernel space.
In this article, we introduce the new linux userspace driver model. Linux dma engine slave api page 1 the dma engine driver works as a layer under the xilinx dma drivers using the slave dma api it appears that slave may refer to the fact that the software initiates the dma transactions to the dma controller hardware rather than a hardware device with integrated dma initiating a transaction. Inputoutput data through the mmapped memory regions. Hardware that is ideally suited for an uio driver fulfills all of the following. These attributes are accessible through sysfs files. Quick and easy device drivers for embedded linux using uio. A custom kernel driver module can add its own attributes to the device owned by the uio driver, but not added to the uio device itself at this time. Whats needed is a way of allocating a chunk of physical memory, mapping it into the usermode process memory space and returning both the physical and the virtual address to the usermode process. I am trying to write a driver for axidma using uio code attached. It permits sharing a part of the memory to the user space and catch a given interrupt without the need of programming a specific kernel driver.
Methods to protect proprietary components in device drivers. This article shows how uio works, and how it performs under realtime conditions. Using this, you only need to write the userspace driver, removing the need to write a hardwarespecific kernel module. User space mappable dma buffer device driver for linux. Additionally, the kernel creates pseudofiles on the sys filesystem, which the userspace part references to learn addresses for access.
My device needs two 128 kb chunks of dma able memory. Interfacing with device drivers continued by chris simmonds. Writing userspace io device driver uio drivers linux provides a standard called uio user io framework for developing userspacebased device drivers. I can control dma usnig uio driver, i used your kernel module, comiled and loaded, it appered in devmemalloc. The device driver enables usermode software to memorymap the. In the end the only way to make pci fast is with dma and the only way to dma is with custom kernel drivers under linux in order to get access to dma capable memory. Contribute to rumpkernelwiki development by creating an account on github. Driver shift userspace drivers in the new linux kernel. Userspace driver future uio is a good start uio primarily needs support for dma to en able a broader range of drivers driverspecific memory allocation and region characteristic info plan is to convert this driver to a uio driver with dma helper extensions some thought still required on how to properly abstract these extensions need an open userspace dma driver example. Simple axi dma linux driver example with no scatter gather. Via ioctl it provides a mechanism to map msix interrupts into event file descriptors similar to vfio.
Pci express reference designs and application notes. Also the device needs to support it, therefore i had to implement a dma engine. The linux uio drivers at driversuio in the kernel tree do not provide any facilities for the usermode side to set up dma buffers. The pci bus implementation for linux uses the userspace io kernel api to access the bus. Ive had luck writing a dmacapable driver almost completely in user space. This might change in the future if it would be found to be useful. I can control dma usnig uio driver, i used your kernel module, comiled and.