Question

我正在为LCD显示器编写驱动程序。根据应用笔记，我需要定期向命令写一个伪SPI写，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。

然而，出现问题是因为spi_write函数导致完整的内核崩溃并出现以下错误：

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

基于以下帖子： How to solve "BUG: scheduling while atomic: swapper /0x00000103/0, CPU#0"? in TSC2007 Driver?

“原子调度”表示您已尝试睡眠在某个你不应该的地方 - 比如在一个受螺旋锁保护的地方临界区或中断处理程序。

也许对spi_write的调用会触发某种睡眠行为。禁止在这里睡觉是有意义的，因为基于堆栈跟踪，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，SPI事务需要定期发生？

以下是计时器处理程序的摘要（虽然有一些手动修改，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想出的。很好地工作，但使用delayed_work涉及必须跳过一些箍。

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);
}

Answer 1

如果查看spi_write源代码，则会调用spi_sync，如果查看第一行 spi_sync - ＆gt; mutex_lock，所以spi_write无法在中断内运行，并且无法通过.config或sysfs进行修复。

我的问题是：实现这种周期性行为的正确方法是什么，其中＆gt; SPI交易需要定期发生吗？

答案取决于您的硬件，您希望通过SPI发送数据的频率，你接受的延迟等等。

你可以在workqueue回调中使用spi_write，参见 https://www.safaribooksonline.com/library/view/understanding-the-linux/0596005652/ch04s08.html

专为此类事物设计的工作队列（运行无法在中断上下文中运行的东西），

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

如果延迟无关紧要，您也可以将事物移动到用户空间，并通过spidev接口写入SPI。

在linux驱动程序中定期调用spi_write

1 个答案: