linux spi

linux spi

spi_sync()执行流程?
spi_async()执行流程?
spi peripheral driver中，调用spi_sync() 为什么会看到spi* 内核线程会有负载？

int spi_sync(struct spi_device *spi, struct spi_message *message)
{
	int ret;

	mutex_lock(&spi->controller->bus_lock_mutex);
	ret = __spi_sync(spi, message);
	mutex_unlock(&spi->controller->bus_lock_mutex);

	return ret;
}
EXPORT_SYMBOL_GPL(spi_sync);

可以看到__spi_sync() 加了mutex, 不会多线程并发；

一般spi controler driver，会实现

		ctrl->prepare_transfer_hardware = soc_spi_prepare_xfer_hardware;
		ctrl->transfer_one = soc_spi_transfer_one;
		ctrl->unprepare_transfer_hardware = soc_spi_unprepare_xfer_hardware;

spi 硬件传输ops func;

不会实现ctlr->transfer ops func;

spi_register_controller()
| spi_controller_initialize_queue()

static int spi_controller_initialize_queue(struct spi_controller *ctlr)
{
	int ret;

	ctlr->transfer = spi_queued_transfer;
	if (!ctlr->transfer_one_message)
		ctlr->transfer_one_message = spi_transfer_one_message;

	/* Initialize and start queue */
	ret = spi_init_queue(ctlr);
	if (ret) {
		dev_err(&ctlr->dev, "problem initializing queue\n");
		goto err_init_queue;
	}
	ctlr->queued = true;
	ret = spi_start_queue(ctlr);
	if (ret) {
		dev_err(&ctlr->dev, "problem starting queue\n");
		goto err_start_queue;
	}

	return 0;

err_start_queue:
	spi_destroy_queue(ctlr);
err_init_queue:
	return ret;
}

有：
ctlr->transfer = spi_queued_transfer;
ctlr->transfer_one_message = spi_transfer_one_message;
spi_init_queue()中，kthread_run kworker_task;

static void spi_complete(void *arg)
{
	complete(arg);
}

static int __spi_sync(struct spi_device *spi, struct spi_message *message)
{
	DECLARE_COMPLETION_ONSTACK(done);
	int status;
	struct spi_controller *ctlr = spi->controller;
	unsigned long flags;

	status = __spi_validate(spi, message);
	if (status != 0)
		return status;

	message->complete = spi_complete;
	message->context = &done;
	message->spi = spi;

	SPI_STATISTICS_INCREMENT_FIELD(&ctlr->statistics, spi_sync);
	SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_sync);

	/* If we're not using the legacy transfer method then we will
	 * try to transfer in the calling context so special case.
	 * This code would be less tricky if we could remove the
	 * support for driver implemented message queues.
	 */
	if (ctlr->transfer == spi_queued_transfer) {
		spin_lock_irqsave(&ctlr->bus_lock_spinlock, flags);

		trace_spi_message_submit(message);

		status = __spi_queued_transfer(spi, message, false);

		spin_unlock_irqrestore(&ctlr->bus_lock_spinlock, flags);
	} else {
		status = spi_async_locked(spi, message);
	}

	if (status == 0) {
		/* Push out the messages in the calling context if we
		 * can.
		 */
		if (ctlr->transfer == spi_queued_transfer) {
			SPI_STATISTICS_INCREMENT_FIELD(&ctlr->statistics,
						       spi_sync_immediate);
			SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics,
						       spi_sync_immediate);
			__spi_pump_messages(ctlr, false);
		}

		wait_for_completion(&done);
		status = message->status;
	}
	message->context = NULL;
	return status;
}

调用：
__spi_queued_transfer()
__spi_pump_messages()
wait_for_completion()

static int __spi_queued_transfer(struct spi_device *spi,
				 struct spi_message *msg,
				 bool need_pump)
{
	struct spi_controller *ctlr = spi->controller;
	unsigned long flags;

	spin_lock_irqsave(&ctlr->queue_lock, flags);

	if (!ctlr->running) {
		spin_unlock_irqrestore(&ctlr->queue_lock, flags);
		return -ESHUTDOWN;
	}
	msg->actual_length = 0;
	msg->status = -EINPROGRESS;

	list_add_tail(&msg->queue, &ctlr->queue);
	if (!ctlr->busy && need_pump)
		kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages);

	spin_unlock_irqrestore(&ctlr->queue_lock, flags);
	return 0;
}

__spi_sync()->__spi_queued_transfer(spi, message, false);
spi_message 加入ctlr->queue；
注意这里need_pump:false;
并不会唤醒spi* 内核线程 执行work;

__spi_sync()
|__spi_queued_transfer(spi, message, false);
|__spi_pump_messages(ctlr, false)---> ctlr->transfer_one_message(ctlr, ctlr->cur_msg);
|wait_for_completion(&done);

static int spi_transfer_one_message(struct spi_controller *ctlr,
				    struct spi_message *msg)
{
	struct spi_transfer *xfer;
	bool keep_cs = false;
	int ret = 0;
	unsigned long long ms = 1;
	struct spi_statistics *statm = &ctlr->statistics;
	struct spi_statistics *stats = &msg->spi->statistics;

	spi_set_cs(msg->spi, true);

	SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
	SPI_STATISTICS_INCREMENT_FIELD(stats, messages);

	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
		trace_spi_transfer_start(msg, xfer);

		spi_statistics_add_transfer_stats(statm, xfer, ctlr);
		spi_statistics_add_transfer_stats(stats, xfer, ctlr);

		if (xfer->tx_buf || xfer->rx_buf) {
			reinit_completion(&ctlr->xfer_completion);

			ret = ctlr->transfer_one(ctlr, msg->spi, xfer);
			if (ret < 0) {
				SPI_STATISTICS_INCREMENT_FIELD(statm,
							       errors);
				SPI_STATISTICS_INCREMENT_FIELD(stats,
							       errors);
				dev_err(&msg->spi->dev,
					"SPI transfer failed: %d\n", ret);
				goto out;
			}

			if (ret > 0) {
				ret = 0;
				ms = 8LL * 1000LL * xfer->len;
				do_div(ms, xfer->speed_hz);
				ms += ms + 200; /* some tolerance */

				if (ms > UINT_MAX)
					ms = UINT_MAX;

				ms = wait_for_completion_timeout(&ctlr->xfer_completion,
								 msecs_to_jiffies(ms));
			}

			if (ms == 0) {
				SPI_STATISTICS_INCREMENT_FIELD(statm,
							       timedout);
				SPI_STATISTICS_INCREMENT_FIELD(stats,
							       timedout);
				dev_err(&msg->spi->dev,
					"SPI transfer timed out\n");
				msg->status = -ETIMEDOUT;
			}
		} else {
			if (xfer->len)
				dev_err(&msg->spi->dev,
					"Bufferless transfer has length %u\n",
					xfer->len);
		}

		trace_spi_transfer_stop(msg, xfer);

		if (msg->status != -EINPROGRESS)
			goto out;

		if (xfer->delay_usecs) {
			u16 us = xfer->delay_usecs;

			if (us <= 10)
				udelay(us);
			else
				usleep_range(us, us + DIV_ROUND_UP(us, 10));
		}

		if (xfer->cs_change) {
			if (list_is_last(&xfer->transfer_list,
					 &msg->transfers)) {
				keep_cs = true;
			} else {
				spi_set_cs(msg->spi, false);
				udelay(10);
				spi_set_cs(msg->spi, true);
			}
		}

		msg->actual_length += xfer->len;
	}

out:
	if (ret != 0 || !keep_cs)
		spi_set_cs(msg->spi, false);

	if (msg->status == -EINPROGRESS)
		msg->status = ret;

	if (msg->status && ctlr->handle_err)
		ctlr->handle_err(ctlr, msg);

	spi_res_release(ctlr, msg);

	spi_finalize_current_message(ctlr);

	return ret;
}

__spi_sync()
|__spi_queued_transfer(spi, message, false);
|__spi_pump_messages(ctlr, false)---> ctlr->transfer_one_message(ctlr, ctlr->cur_msg);
____| spi_set_cs(msg->spi, true);
____| ret = ctlr->transfer_one(ctlr, msg->spi, xfer); /* spi controller transfer ops /
____| spi_set_cs(msg->spi, false);
____| spi_finalize_current_message(ctlr);
________| kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages); / 关键点 */
________| mesg->complete(mesg->context);
|wait_for_completion(&done);

关键是：

void spi_finalize_current_message(struct spi_controller *ctlr)
{
	struct spi_message *mesg;
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&ctlr->queue_lock, flags);
	mesg = ctlr->cur_msg;
	spin_unlock_irqrestore(&ctlr->queue_lock, flags);

	spi_unmap_msg(ctlr, mesg);

	if (ctlr->cur_msg_prepared && ctlr->unprepare_message) {
		ret = ctlr->unprepare_message(ctlr, mesg);
		if (ret) {
			dev_err(&ctlr->dev, "failed to unprepare message: %d\n",
				ret);
		}
	}

	spin_lock_irqsave(&ctlr->queue_lock, flags);
	ctlr->cur_msg = NULL;
	ctlr->cur_msg_prepared = false;
	kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages);
	spin_unlock_irqrestore(&ctlr->queue_lock, flags);

	trace_spi_message_done(mesg);

	mesg->state = NULL;
	if (mesg->complete)
		mesg->complete(mesg->context);
}

spi_finalize_current_message()-> kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages);

spi kthread 执行work:

static void __spi_pump_messages(struct spi_controller *ctlr, bool in_kthread)
{
	unsigned long flags;
	bool was_busy = false;
	int ret;

	/* Lock queue */
	spin_lock_irqsave(&ctlr->queue_lock, flags);

	/* Make sure we are not already running a message */
	if (ctlr->cur_msg) {
		spin_unlock_irqrestore(&ctlr->queue_lock, flags);
		return;
	}

	/* If another context is idling the device then defer */
	if (ctlr->idling) {
		kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages);
		spin_unlock_irqrestore(&ctlr->queue_lock, flags);
		return;
	}

	/* Check if the queue is idle */
	if (list_empty(&ctlr->queue) || !ctlr->running) {
		if (!ctlr->busy) {
			spin_unlock_irqrestore(&ctlr->queue_lock, flags);
			return;
		}

		/* Only do teardown in the thread */
		if (!in_kthread) {
			kthread_queue_work(&ctlr->kworker,
					   &ctlr->pump_messages);
			spin_unlock_irqrestore(&ctlr->queue_lock, flags);
			return;
		}

		ctlr->busy = false;
		ctlr->idling = true;
		spin_unlock_irqrestore(&ctlr->queue_lock, flags);

		kfree(ctlr->dummy_rx);
		ctlr->dummy_rx = NULL;
		kfree(ctlr->dummy_tx);
		ctlr->dummy_tx = NULL;
		if (ctlr->unprepare_transfer_hardware &&
		    ctlr->unprepare_transfer_hardware(ctlr))
			dev_err(&ctlr->dev,
				"failed to unprepare transfer hardware\n");
		if (ctlr->auto_runtime_pm) {
			pm_runtime_mark_last_busy(ctlr->dev.parent);
			pm_runtime_put_autosuspend(ctlr->dev.parent);
		}
		trace_spi_controller_idle(ctlr);

		spin_lock_irqsave(&ctlr->queue_lock, flags);
		ctlr->idling = false;
		spin_unlock_irqrestore(&ctlr->queue_lock, flags);
		return;
	}

	/* Extract head of queue */
	ctlr->cur_msg =
		list_first_entry(&ctlr->queue, struct spi_message, queue);

	list_del_init(&ctlr->cur_msg->queue);
	if (ctlr->busy)
		was_busy = true;
	else
		ctlr->busy = true;
	spin_unlock_irqrestore(&ctlr->queue_lock, flags);

	mutex_lock(&ctlr->io_mutex);

	if (!was_busy && ctlr->auto_runtime_pm) {
		ret = pm_runtime_get_sync(ctlr->dev.parent);
		if (ret < 0) {
			pm_runtime_put_noidle(ctlr->dev.parent);
			dev_err(&ctlr->dev, "Failed to power device: %d\n",
				ret);
			mutex_unlock(&ctlr->io_mutex);
			return;
		}
	}

	if (!was_busy)
		trace_spi_controller_busy(ctlr);

	if (!was_busy && ctlr->prepare_transfer_hardware) {
		ret = ctlr->prepare_transfer_hardware(ctlr);
		if (ret) {
			dev_err(&ctlr->dev,
				"failed to prepare transfer hardware\n");

			if (ctlr->auto_runtime_pm)
				pm_runtime_put(ctlr->dev.parent);
			mutex_unlock(&ctlr->io_mutex);
			return;
		}
	}

	trace_spi_message_start(ctlr->cur_msg);

	if (ctlr->prepare_message) {
		ret = ctlr->prepare_message(ctlr, ctlr->cur_msg);
		if (ret) {
			dev_err(&ctlr->dev, "failed to prepare message: %d\n",
				ret);
			ctlr->cur_msg->status = ret;
			spi_finalize_current_message(ctlr);
			goto out;
		}
		ctlr->cur_msg_prepared = true;
	}

	ret = spi_map_msg(ctlr, ctlr->cur_msg);
	if (ret) {
		ctlr->cur_msg->status = ret;
		spi_finalize_current_message(ctlr);
		goto out;
	}

	ret = ctlr->transfer_one_message(ctlr, ctlr->cur_msg);
	if (ret) {
		dev_err(&ctlr->dev,
			"failed to transfer one message from queue\n");
		goto out;
	}

out:
	mutex_unlock(&ctlr->io_mutex);

	/* Prod the scheduler in case transfer_one() was busy waiting */
	if (!ret)
		cond_resched();
}

再看下__spi_sync() 代码，发起下一次__spi_sync(), 很可能就是在 spi kthread work中发起spi 控制器数据传输；
特别是spi_sync操作频繁的情况；一些spi_sync()执行过程，只是把spi_msg加入传输queue, kthread 中发起spi控制器传输操作；这样在多核soc中，传输效率提高；

调试，注释掉spi_finalize_current_message()->kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages);操作；
spi_sync() 就都在 spi外设驱动进程（非 spi* 内核线程)执行了；

spi_async() 依赖 kthread_queue_work（） 这个操作；

spi_async() ->__spi_queued_transfer(spi, msg, true) -> list_add_tail(&msg->queue, &ctlr->queue) ->kthread_queue_work(&ctlr->kworker, &ctlr->pump_messages);
代码比较简单；
把spi message加入ctlr->queue; kthread_queue_work;

written by wang_yangkai@163.com
转载请注明author、出处.