编写一段异步DMA的驱动代码

以下是一个简单的异步DMA驱动代码示例，用于从一个外设（如ADC）中读取数据并将其传输到内存中：

#include <linux/module.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/dmaengine.h>
#include <linux/dma-mapping.h>

#define DMA_CHAN_NAME "my_dma_chan"
#define DMA_BUF_SIZE 1024

struct my_device {
    struct platform_device *pdev;
    struct dma_chan *chan;
    dma_addr_t dma_buf_phys;
    void *dma_buf_virt;
};

static int my_device_probe(struct platform_device *pdev)
{
    struct my_device *dev;
    struct dma_chan *chan;
    struct dma_slave_config config;
    dma_cap_mask_t mask;
    int ret;

    dev = devm_kzalloc(&pdev->dev, sizeof(*dev), GFP_KERNEL);
    if (!dev)
        return -ENOMEM;

    dev->pdev = pdev;

    /* Allocate DMA buffer */
    dev->dma_buf_virt = dma_alloc_coherent(&pdev->dev, DMA_BUF_SIZE,
                                           &dev->dma_buf_phys, GFP_KERNEL);
    if (!dev->dma_buf_virt)
        return -ENOMEM;

    /* Get DMA channel */
    dma_cap_zero(mask);
    dma_cap_set(DMA_SLAVE, mask);
    chan = dma_request_channel(mask, NULL, NULL);
    if (!chan) {
        dev_err(&pdev->dev, "failed to get DMA channel\n");
        return -ENODEV;
    }

    /* Configure DMA channel */
    memset(&config, 0, sizeof(config));
    config.direction = DMA_DEV_TO_MEM;
    config.dst_addr = dev->dma_buf_phys;
    config.dst_maxburst = 1;
    config.dst_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;
    config.src_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;
    ret = dmaengine_slave_config(chan, &config);
    if (ret) {
        dev_err(&pdev->dev, "failed to configure DMA channel: %d\n", ret);
        dma_release_channel(chan);
        return ret;
    }

    dev->chan = chan;

    /* Start DMA transfer */
    ret = dmaengine_submit(dev->chan, DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
    if (ret) {
        dev_err(&pdev->dev, "failed to submit DMA transfer: %d\n", ret);
        dma_release_channel(dev->chan);
        return ret;
    }

    /* Enable DMA interrupts */
    dmaengine_irq_enable(dev->chan, DMA_IRQ_MASK_COMPLETE);

    return 0;
}

static int my_device_remove(struct platform_device *pdev)
{
    struct my_device *dev = platform_get_drvdata(pdev);

    /* Disable DMA interrupts */
    dmaengine_irq_disable(dev->chan, DMA_IRQ_MASK_COMPLETE);

    /* Stop DMA transfer */
    dmaengine_terminate_all(dev->chan);

    /* Release DMA channel */
    dma_release_channel(dev->chan);

    /* Free DMA buffer */
    dma_free_coherent(&pdev->dev, DMA_BUF_SIZE, dev->dma_buf_virt, dev->dma_buf_phys);

    return 0;
}

static struct platform_driver my_device_driver = {
    .driver = {
        .name = "my_device",
    },
    .probe = my_device_probe,
    .remove = my_device_remove,
};

module_platform_driver(my_device_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("Asynchronous DMA driver for my_device"); 

在这个示例中，我们使用了DMA引擎框架来管理DMA通道和传输。首先，在驱动的`probe`函数中，我们分配了一个DMA缓冲区，并使用`dma_alloc_coherent`函数将其映射到物理内存中。然后，我们使用`dma_request_channel`函数获取一个DMA通道，并使用`dmaengine_slave_config`函数对其进行配置。最后，我们使用`dmaengine_submit`函数提交DMA传输，并使用`dmaengine_irq_enable`函数启用DMA中断。

在驱动的`remove`函数中，我们关闭DMA中断，停止DMA传输并释放DMA通道和DMA缓冲区。

请注意，这只是一个简单的示例，实际的异步DMA驱动可能需要更多的配置和错误检查。