We are used to controlling our custom AXI4-Full/Lite IP through UIO driver, but not AXI4-Stream IP. Because AXI4-Stream IP has different architecture(customStreamIP.jpg), the UIO device node will not be created. Instead, DMA controler will appearing, and UIO driver can't adapt this situation. As a result, we decide to make a little modification on UIO driver and make a little tricky setting in devicetree file. After modifying, we can control our custom AXI4-Stream IP through UIO driver.

1. Specify which dmaengine-compatible DMA channels you'd like to create userspace-accessible device files for in your device tree:

   udma0 {
       compatible = "generic-uio";
       dmas = <&loopback_dma 0 &loopback_dma 1>;
       dma-names = "loop_tx", "loop_rx";
       udma,dirs = <2 1>;      // direction of DMA channel: 
                               //   1 = RX (dev->cpu), 2 = TX (cpu->dev)
   };
   

For now, udma only support two channel device(one s2mm and one mm2s), please ensure the device node get the correct reference of dma channel.

2. After booting Linux, uio node will become available,

       /dev/uioX
   

3. Sending data is as simple as:

       int xfer_size = 16;
       uint32_t tx_buf[xfer_xize], rx_buf[xfersize];
       int fd = open("/dev/uio0", O_RDWR | O_SYNC);
   
       write(fd, tx_buf, xfer_size);    // send a DMA transaction
       read (fd, rx_buf, xfer_size);
   

We make a little modification on uio.c and uio_pdrv_genirq.c, so we need to replace these two files. Further, we add udma.c and udma.h, please put udma.c under "KERNEL_DIR/drivers/uio/" and udma.h under "KERNEL_DIR/include/linux/". After recompiling, you will get a Linux Kernel with UIO drvier supporting AXI DMA.

We will write a shell script to help users doing these works including creating a virtual device node in devicetree file, replacing and adding files in Linux Kernel directory, compiling kernel, and generating boot files.

Copyright (C) 2018 Billy Liu

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