On Thu, May 21, 2015 at 09:34:03PM -0400, Jeremy Trimble wrote:
> Hello all,
>
> I've written a kernel module that allows data to be sent to or received from
> any DMA device that supports the dmaengine API, using simple read()/write()
> calls from userspace.
>
> Motivation:
>
> While doing some work for my master's thesis recently using the Xilinx Zynq
> SoC, I needed a way to stream test data into and out of an FPGA soft-core I was
> developing. I was using the Xilinx AXI DMA soft-core (and its
> dmaengine-compatible driver that I believe is related to Kedareswara rao
> Appana's patch submitted recently).
>
> Although dmaengine provides a versatile in-kernel API, to my knowledge there's
> no direct userspace interface for the case where one wants to simply
> send/receive data through a slave dma channel -- writing a separate
> userspace-facing module would be required. (Or some hack using /dev/kmem.)
why not use dmatest?
--
~Vinod
>
> Usage:
>
> The ezdma ("easy DMA") module implements a read()/write() interface for
> receiving/sending data through any slave DMA channel.
>
> It is configured using the device tree:
>
> 1. Include a node like below into the device tree:
>
> ezdma0 {
> compatible = "ezdma";
> dmas = <&loopback_dma 0 &loopback_dma 1>;
> dma-names = "loop_tx", "loop_rx";
> ezdma,dirs = <2 1>; // direction of DMA channel:
> // 1 = RX (dev->cpu), 2 = TX (cpu->dev)
> };
>
> 2. After inserting the ezdma module, two devices, as named in your dma-names
> above, will become available:
>
> /dev/loop_tx
> /dev/loop_rx
>
> 3. Sending data is as easy as:
>
> int tx_fd = open("/dev/loop_tx", O_WRONLY);
> int rx_fd = open("/dev/loop_rx", O_RDONLY);
>
> write(tx_fd, tx_buf, xfer_size); // send a DMA transaction
> read (rx_fd, rx_buf, xfer_size);
>
> Currently, each read()/write() call causes a single transfer to occur in the
> underlying slave DMA channel, but support could be added for readv()/writev()
> as well.
>
> Notes:
>
> Although in my case I was using it with the AXI DMA to send and receive
> AXI4-Stream packets, there is no dependency on any particular dmaengine driver
> or hardware; it *should* work with any device that has a dmaengine driver.
>
> I think it might be useful to others as an engineering/research tool.
>
> I'm cleaning up the code and intend to submit it as a patch to this list in the
> coming days. Though I've been writing kernel code for a few years now, this
> will be my first patch going upstream. I appreciate any feedback.
>
> Currently, I've posted my original code (before cleanup) here:
> https://github.com/jeremytrimble/ezdma
>
> Also, I'm open to changing the name if "ezdma" isn't seen as descriptive.
>
>
> Cheers.
>
> -Jeremy Trimble
> --
> To unsubscribe from this list: send the line "unsubscribe dmaengine" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
--
To unsubscribe from this list: send the line "unsubscribe dmaengine" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
