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我正在为 LCD 显示器编写驱动程序。根据应用说明，我需要定期向命令写入一个虚拟 SPI 写入以最大化其对比度。为此，我设置了一个计时器并尝试从计时器处理程序中编写对比度最大化的 2 字节虚拟命令。

但是，出现了问题，因为 spi_write 函数导致内核完全崩溃并出现以下错误：

BUG: scheduling while atomic: swapper/1/0/0x00000102

基于以下帖子： 如何解决“BUG：原子时调度：交换器/0x00000103/0，CPU#0”？在 TSC2007 驱动程序中？

“Scheduling while atomic”表示你试图在不应该的地方睡觉——比如在自旋锁保护的关键部分或中断处理程序中。

也许对 spi_write 的调用会触发某种睡眠行为。在这里禁止休眠是有意义的，因为根据堆栈跟踪，我看到代码处于软 IRQ 状态：

[<404ec600>] (schedule_timeout) from [<404eac3c>] (wait_for_common+0x114/0x15c)
[<404eac3c>] (wait_for_common) from [<4031c7a4>] (spi_sync+0x70/0x88)
[<4031c7a4>] (spi_sync) from [<3f08a6b0>] (plt_lcd_send_toggle_comin_cmd+0x7c/0x84 [plt_lcd_spi])
[<3f08a6b0>] (plt_lcd_send_toggle_comin_cmd [plt_lcd_spi]) from [<3f08a6c4>] (plt_lcd_timer_handler+0xc/0x2c [plt_lcd_spi])
[<3f08a6c4>] (plt_lcd_timer_handler [plt_lcd_spi]) from [<40058818>] (call_timer_fn.isra.26+0x20/0x30)
[<40058818>] (call_timer_fn.isra.26) from [<40058f30>] (run_timer_softirq+0x1ec/0x21c)
[<40058f30>] (run_timer_softirq) from [<40023414>] (__do_softirq+0xe0/0x1c8)
[<40023414>] (__do_softirq) from [<400236f0>] (irq_exit+0x58/0xac)
[<400236f0>] (irq_exit) from [<4004ee4c>] (__handle_domain_irq+0x80/0xa0)
[<4004ee4c>] (__handle_domain_irq) from [<400085ac>] (gic_handle_irq+0x38/0x5c)
[<400085ac>] (gic_handle_irq) from [<40011740>] (__irq_svc+0x40/0x74)

我的问题是：实现这种周期性行为的正确方法是什么，需要定期发生 SPI 事务？

以下是计时器处理程序的摘要（尽管进行了一些手动修改以使名称更通用——我可能在过程中插入了一些拼写错误）

static void lcd_timer_handler(unsigned long data)
{
    // priv is a private structure that contains private info for the 
    // driver: timer structure, timer timeout, context for the dummy command
    lcd_priv * const priv = (memlcd_priv *) data;

    unsigned char dummy[2];
    dummy[0] = get_dummy_command_code(priv);
    dummy[1] = 0; // command must be terminated by a 0.

    // This is the call that causes the failure.
    // priv->spi is a struct spi_device *
    spi_write(priv->spi, ((const void *) dummy), 2);

    // Re-arm the timer
    mod_timer(&priv->timer, jiffies + priv->timer_timeout);
}

谢谢！

编辑：这是我在实施以下答案中的建议后得出的结论。工作得很好，但使用延迟工作涉及必须跳过几圈。

typedef struct lcd_priv {
    /* private stuff: */
    /* ... */

    /* workqueue stuff: */
    struct workqueue_struct * wq;
    struct delayed_work periodic_work;
} lcd_priv;


void lcd_periodic_work(struct work_struct * work_struct_ptr)
{
    /*
     * Old documentation refers to a "data" pointer, but the API
     * no longer supports it. The developer is invited to put the work_struct
     * inside what would have been pointed to by "data" and to use container_of()
     * to recover this master struct.
     * See http://lwn.net/Articles/211279/ for more info.
    */

    struct delayed_work * delayed = container_of(work_struct_ptr, struct delayed_work, work);
    lcd_priv * priv = container_of(delayed, lcd_priv, periodic_work);

    /* (prepare spi buffer in priv->spi_buf) */
    /* ... */

    /* This could be any activity that goes to sleep: */
    spi_write(priv->spi, ((const void *) &priv->spi_buf[0]), 2);

    queue_delayed_work(priv->wq, &priv->periodic_work, TOGGLE_FREQUENCY);
}

static void lcd_start_workqueue(lcd_priv * const priv) {
    priv->wq = create_singlethread_workqueue("lcd_periodic_st_wq");

    INIT_DELAYED_WORK(&priv->periodic_work, lcd_periodic_work);
    queue_delayed_work(priv->wq, &priv->periodic_work, TOGGLE_FREQUENCY);
}

static void lcd_stop_workqueue(lcd_priv * const priv) {
    destroy_workqueue(priv->wq);
}
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1 回答 1

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如果看spi_write源码，它调用spi_sync，如果看 spi_sync->的第一行mutex_lock，所以spi_write不能在interrupt里面运行，也不能通过.configor来修复sysfs。

我的问题是：实现这种周期性行为的正确方法是什么，哪里需要定期发生 SPI 事务？

答案取决于您的硬件、您希望通过 SPI 发送数据的频率、您接受的延迟等。

您可以spi_write在工作队列回调中使用，请参阅 https://www.safaribooksonline.com/library/view/understanding-the-linux/0596005652/ch04s08.html

专门为这类事情设计的工作队列（运行不能在中断上下文中运行的东西），

您也可以使用spi_async通过 spi 安排写入。spy_async可以在中断处理程序中调用。

如果延迟无关紧要，您也可以将内容移至用户空间，并通过spidev接口写入 SPI。

于 2016-05-10T22:30:55.350 回答