How to make a DMA transfer?

[itzikhai]

What is the purpose of the driver ?
How it can be used to really transfer the buffer using a DMA ? Isn't it an architecture dependent ?
Why it is depended only at ARM ?
For example, using PPC chip with a PCIe device.

[KAWAZOME Ichiro]

Thank you for the issue.

The purpose of this driver is to provide a DMA buffer that can be accessed by the CPU.
udmabuf does not control DMA. It is the job of the user program.

The architecture is limited to ARM / ARM64 because I have only verified operation on those architectures. I have not checked if it works on other architectures.

[itzikhai]

Hello ikwzm.

Thanks for your replies.

You mean that control DMA is the part of driver - right?
Is is possible to control DMA at userspace program?

Regarding the arch. - I may be able modify, compile and build your device driver at PPC64 based on NXP B4860.

[KAWAZOME Ichiro]

You can use uio and udmabuf to do DMA transfers without writing a kernel driver.

For example, in the following example, DMA transfer is performed with a program written in Python.

https://github.com/ikwzm/ZynqMP-FPGA-Linux-Example-2-Ultra96

[noelpedro]

Hi guys I'm trying to use udmabuf on a simple loopback design here is my device tree that I plan to use:

Do I need to define memory region of udmabuf nodes for RX and TX dma channels?
`

/ {
/* Loopback DMA setup */

loopback_dma: axidma@40400000 {
    compatible = "generic-uio";
    #dma-cells = <1>;
    reg = < 0x40400000 0x10000 >;
    clocks = <&clkc 15>, <&clkc 15>, <&clkc 15>, <&clkc 15>; // fclk0 from clock controller
    clock-names = "s_axi_lite_aclk", "m_axi_mm2s_aclk", "m_axi_s2mm_aclk", "m_axi_sg_aclk";
    xlnx,include-sg;

    loopback_dma_mm2s_chan: dma-channel@40400000 {
        compatible = "xlnx,axi-dma-mm2s-channel";
        interrupt-parent = <&intc>;
        interrupts = <0 31 4>; 
        xlnx,datawidth = <0x20>;        
        xlnx,sg-length-width = <14>;    

        xlnx,device-id = <0x1>;     
    };

    loopback_dma_s2mm_chan: dma-channel@40400030 {
        compatible = "xlnx,axi-dma-s2mm-channel";
        interrupt-parent = <&intc>;
        interrupts = <0 32 4>; 
        xlnx,datawidth = <0x20>;       
        xlnx,sg-length-width = <14>;    
        xlnx,device-id = <0x1>;     
    };
};

udmabuf@0x00 {
compatible = "ikwzm,udmabuf-0.10.a";
device-name = "udmabuf0";
minor-number = <0>;
size = <0x00100000>;
sync-direction = <1>; //TX
};
udmabuf@0x00 {
compatible = "ikwzm,udmabuf-0.10.a";
device-name = "udmabuf1";
minor-number = <0>;
size = <0x00100000>;
sync-direction = <2>; //RX
};

};
`