dmatest.c

这个代码位于/driver/dma/dmatest.c， 可以编译成模块 dmatest.ko

1. late_initcall(dmatest_init) ---这个init还是第一次见。

static int __init dmatest_init(void)
{
	dma_cap_mask_t mask;
	struct dma_chan *chan;
	int err = 0;

	dma_cap_zero(mask);        //清除mask
	dma_cap_set(DMA_MEMCPY, mask);                  //设置 DMA_MEMCPY 掩码
	for (;;) {
		chan = dma_request_channel(mask, filter, NULL);   //请求获得 dma channel
		if (chan) {
			err = dmatest_add_channel(chan);               //添加 dma test channel
			if (err) {
				dma_release_channel(chan);               //释放 dma channel
				break; /* add_channel failed, punt */
			}
		} else
			break; /* no more channels available */
		if (max_channels && nr_channels >= max_channels)               //限定最大 channel数
			break; /* we have all we need */
	}

	return err;
}
/* when compiled-in wait for drivers to load first */
late_initcall(dmatest_init);

dma_cap_mask_t

/**
 * dma_cap_mask_t - capabilities bitmap modeled after cpumask_t.
 * See linux/cpumask.h
 */
typedef struct { DECLARE_BITMAP(bits, DMA_TX_TYPE_END); } dma_cap_mask_t;

dma_cap_zero

#define dma_cap_zero(mask) __dma_cap_zero(&(mask))
static inline void __dma_cap_zero(dma_cap_mask_t *dstp)
{
	bitmap_zero(dstp->bits, DMA_TX_TYPE_END);
}

dma_cap_set

#define dma_cap_set(tx, mask) __dma_cap_set((tx), &(mask))
static inline void
__dma_cap_set(enum dma_transaction_type tx_type, dma_cap_mask_t *dstp)
{
	set_bit(tx_type, dstp->bits);
}

2. dma_request_channel() --- 请求获取dma channel

#define dma_request_channel(mask, x, y) __dma_request_channel(&(mask), x, y)

/**
 * dma_request_channel - try to allocate an exclusive channel
 * @mask: capabilities that the channel must satisfy
 * @fn: optional callback to disposition available channels
 * @fn_param: opaque parameter to pass to dma_filter_fn
 */
struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, void *fn_param)
{
	struct dma_device *device, *_d;
	struct dma_chan *chan = NULL;
	int err;

	/* Find a channel */
	mutex_lock(&dma_list_mutex);
	list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
		chan = private_candidate(mask, device, fn, fn_param);
		if (chan) {
			/* Found a suitable channel, try to grab, prep, and
			 * return it.  We first set DMA_PRIVATE to disable
			 * balance_ref_count as this channel will not be
			 * published in the general-purpose allocator
			 */
			dma_cap_set(DMA_PRIVATE, device->cap_mask);
			device->privatecnt++;
			err = dma_chan_get(chan);

			if (err == -ENODEV) {
				pr_debug("%s: %s module removed\n", __func__,
					 dma_chan_name(chan));
				list_del_rcu(&device->global_node);
			} else if (err)
				pr_err("dmaengine: failed to get %s: (%d)\n",
				       dma_chan_name(chan), err);
			else
				break;
			if (--device->privatecnt == 0)
				dma_cap_clear(DMA_PRIVATE, device->cap_mask);
			chan->private = NULL;
			chan = NULL;
		}
	}
	mutex_unlock(&dma_list_mutex);

	pr_debug("%s: %s (%s)\n", __func__, chan ? "success" : "fail",
		 chan ? dma_chan_name(chan) : NULL);

	return chan;
}
EXPORT_SYMBOL_GPL(__dma_request_channel);

3. dmatest_add_channel ---添加 dma test channel

static int dmatest_add_channel(struct dma_chan *chan)
{
	struct dmatest_chan	*dtc;
	struct dma_device	*dma_dev = chan->device;
	unsigned int		thread_count = 0;
	unsigned int		cnt;

	dtc = kmalloc(sizeof(struct dmatest_chan), GFP_KERNEL);
	if (!dtc) {
		pr_warning("dmatest: No memory for %s\n", dma_chan_name(chan));
		return -ENOMEM;
	}

	dtc->chan = chan;
	INIT_LIST_HEAD(&dtc->threads);

	if (dma_has_cap(DMA_MEMCPY, dma_dev->cap_mask)) {
		cnt = dmatest_add_threads(dtc, DMA_MEMCPY);
		thread_count += cnt > 0 ? cnt : 0;
	}
	if (dma_has_cap(DMA_XOR, dma_dev->cap_mask)) {
		cnt = dmatest_add_threads(dtc, DMA_XOR);
		thread_count += cnt > 0 ? cnt : 0;
	}
	if (dma_has_cap(DMA_PQ, dma_dev->cap_mask)) {
		cnt = dmatest_add_threads(dtc, DMA_PQ);
		thread_count += cnt > 0 ?: 0;
	}

	pr_info("dmatest: Started %u threads using %s\n",
		thread_count, dma_chan_name(chan));

	list_add_tail(&dtc->node, &dmatest_channels);
	nr_channels++;

	return 0;
}

4. dmatest_add_threads

static int dmatest_add_threads(struct dmatest_chan *dtc, enum dma_transaction_type type)
{
	struct dmatest_thread *thread;
	struct dma_chan *chan = dtc->chan;
	char *op;
	unsigned int i;

	if (type == DMA_MEMCPY)
		op = "copy";
	else if (type == DMA_XOR)
		op = "xor";
	else if (type == DMA_PQ)
		op = "pq";
	else
		return -EINVAL;

	for (i = 0; i < threads_per_chan; i++) {
		thread = kzalloc(sizeof(struct dmatest_thread), GFP_KERNEL);
		if (!thread) {
			pr_warning("dmatest: No memory for %s-%s%u\n",
				   dma_chan_name(chan), op, i);

			break;
		}
		thread->chan = dtc->chan;
		thread->type = type;
		smp_wmb();
		thread->task = kthread_run(dmatest_func, thread, "%s-%s%u",           //创建新线程，运行dmatest_func 程序。
				dma_chan_name(chan), op, i);
		if (IS_ERR(thread->task)) {
			pr_warning("dmatest: Failed to run thread %s-%s%u\n",
					dma_chan_name(chan), op, i);
			kfree(thread);
			break;
		}

		/* srcbuf and dstbuf are allocated by the thread itself */

		list_add_tail(&thread->node, &dtc->threads);
	}

	return i;
}

5. dmatest_func 这是新创建进程所运行的程序

/*
 * This function repeatedly tests DMA transfers of various lengths and
 * offsets for a given operation type until it is told to exit by
 * kthread_stop(). There may be multiple threads running this function
 * in parallel for a single channel, and there may be multiple channels
 * being tested in parallel.
 *
 * Before each test, the source and destination buffer is initialized
 * with a known pattern. This pattern is different depending on
 * whether it's in an area which is supposed to be copied or
 * overwritten, and different in the source and destination buffers.
 * So if the DMA engine doesn't copy exactly what we tell it to copy,
 * we'll notice.
 */
static int dmatest_func(void *data)
{
	struct dmatest_thread	*thread = data;
	struct dma_chan		*chan;
	const char		*thread_name;
	unsigned int		src_off, dst_off, len;
	unsigned int		error_count;
	unsigned int		failed_tests = 0;
	unsigned int		total_tests = 0;
	dma_cookie_t		cookie;
	enum dma_status		status;
	enum dma_ctrl_flags 	flags;
	u8			pq_coefs[pq_sources + 1];
	int			ret;
	int			src_cnt;
	int			dst_cnt;
	int			i;

	thread_name = current->comm;

	ret = -ENOMEM;

	smp_rmb();
	chan = thread->chan;
	if (thread->type == DMA_MEMCPY)
		src_cnt = dst_cnt = 1;
	else if (thread->type == DMA_XOR) {
		src_cnt = xor_sources | 1; /* force odd to ensure dst = src */
		dst_cnt = 1;
	} else if (thread->type == DMA_PQ) {
		src_cnt = pq_sources | 1; /* force odd to ensure dst = src */
		dst_cnt = 2;
		for (i = 0; i < src_cnt; i++)
			pq_coefs[i] = 1;
	} else
		goto err_srcs;

	thread->srcs = kcalloc(src_cnt+1, sizeof(u8 *), GFP_KERNEL);
	if (!thread->srcs)
		goto err_srcs;
	for (i = 0; i < src_cnt; i++) {
		thread->srcs[i] = kmalloc(test_buf_size, GFP_KERNEL);
		if (!thread->srcs[i])
			goto err_srcbuf;
	}
	thread->srcs[i] = NULL;

	thread->dsts = kcalloc(dst_cnt+1, sizeof(u8 *), GFP_KERNEL);
	if (!thread->dsts)
		goto err_dsts;
	for (i = 0; i < dst_cnt; i++) {
		thread->dsts[i] = kmalloc(test_buf_size, GFP_KERNEL);
		if (!thread->dsts[i])
			goto err_dstbuf;
	}
	thread->dsts[i] = NULL;

	set_user_nice(current, 10);

	flags = DMA_CTRL_ACK | DMA_COMPL_SKIP_DEST_UNMAP | DMA_PREP_INTERRUPT;

	while (!kthread_should_stop()
	       && !(iterations && total_tests >= iterations)) {
		struct dma_device *dev = chan->device;
		struct dma_async_tx_descriptor *tx = NULL;
		dma_addr_t dma_srcs[src_cnt];
		dma_addr_t dma_dsts[dst_cnt];
		struct completion cmp;
		unsigned long tmo = msecs_to_jiffies(3000);
		u8 align = 0;

		total_tests++;

		/* honor alignment restrictions */
		if (thread->type == DMA_MEMCPY)
			align = dev->copy_align;
		else if (thread->type == DMA_XOR)
			align = dev->xor_align;
		else if (thread->type == DMA_PQ)
			align = dev->pq_align;

		if (1 << align > test_buf_size) {
			pr_err("%u-byte buffer too small for %d-byte alignment\n",
			       test_buf_size, 1 << align);
			break;
		}

		len = dmatest_random() % test_buf_size + 1;
		len = (len >> align) << align;
		if (!len)
			len = 1 << align;
		src_off = dmatest_random() % (test_buf_size - len + 1);
		dst_off = dmatest_random() % (test_buf_size - len + 1);

		src_off = (src_off >> align) << align;
		dst_off = (dst_off >> align) << align;

		dmatest_init_srcs(thread->srcs, src_off, len);
		dmatest_init_dsts(thread->dsts, dst_off, len);

		for (i = 0; i < src_cnt; i++) {
			u8 *buf = thread->srcs[i] + src_off;

			dma_srcs[i] = dma_map_single(dev->dev, buf, len,
						     DMA_TO_DEVICE);
		}
		/* map with DMA_BIDIRECTIONAL to force writeback/invalidate */
		for (i = 0; i < dst_cnt; i++) {
			dma_dsts[i] = dma_map_single(dev->dev, thread->dsts[i],
						     test_buf_size,
						     DMA_BIDIRECTIONAL);
		}


		if (thread->type == DMA_MEMCPY)
			tx = dev->device_prep_dma_memcpy(chan,
							 dma_dsts[0] + dst_off,
							 dma_srcs[0], len,
							 flags);
		else if (thread->type == DMA_XOR)
			tx = dev->device_prep_dma_xor(chan,
						      dma_dsts[0] + dst_off,
						      dma_srcs, src_cnt,
						      len, flags);
		else if (thread->type == DMA_PQ) {
			dma_addr_t dma_pq[dst_cnt];

			for (i = 0; i < dst_cnt; i++)
				dma_pq[i] = dma_dsts[i] + dst_off;
			tx = dev->device_prep_dma_pq(chan, dma_pq, dma_srcs,
						     src_cnt, pq_coefs,
						     len, flags);
		}

		if (!tx) {
			for (i = 0; i < src_cnt; i++)
				dma_unmap_single(dev->dev, dma_srcs[i], len,
						 DMA_TO_DEVICE);
			for (i = 0; i < dst_cnt; i++)
				dma_unmap_single(dev->dev, dma_dsts[i],
						 test_buf_size,
						 DMA_BIDIRECTIONAL);
			pr_warning("%s: #%u: prep error with src_off=0x%x "
					"dst_off=0x%x len=0x%x\n",
					thread_name, total_tests - 1,
					src_off, dst_off, len);
			msleep(100);
			failed_tests++;
			continue;
		}

		init_completion(&cmp);
		tx->callback = dmatest_callback;
		tx->callback_param = &cmp;
		cookie = tx->tx_submit(tx);

		if (dma_submit_error(cookie)) {
			pr_warning("%s: #%u: submit error %d with src_off=0x%x "
					"dst_off=0x%x len=0x%x\n",
					thread_name, total_tests - 1, cookie,
					src_off, dst_off, len);
			msleep(100);
			failed_tests++;
			continue;
		}
		dma_async_issue_pending(chan);

		tmo = wait_for_completion_timeout(&cmp, tmo);
		status = dma_async_is_tx_complete(chan, cookie, NULL, NULL);

		if (tmo == 0) {
			pr_warning("%s: #%u: test timed out\n",
				   thread_name, total_tests - 1);
			failed_tests++;
			continue;
		} else if (status != DMA_SUCCESS) {
			pr_warning("%s: #%u: got completion callback,"
				   " but status is \'%s\'\n",
				   thread_name, total_tests - 1,
				   status == DMA_ERROR ? "error" : "in progress");
			failed_tests++;
			continue;
		}

		/* Unmap by myself (see DMA_COMPL_SKIP_DEST_UNMAP above) */
		for (i = 0; i < dst_cnt; i++)
			dma_unmap_single(dev->dev, dma_dsts[i], test_buf_size,
					 DMA_BIDIRECTIONAL);

		error_count = 0;

		pr_debug("%s: verifying source buffer...\n", thread_name);
		error_count += dmatest_verify(thread->srcs, 0, src_off,
				0, PATTERN_SRC, true);
		error_count += dmatest_verify(thread->srcs, src_off,
				src_off + len, src_off,
				PATTERN_SRC | PATTERN_COPY, true);
		error_count += dmatest_verify(thread->srcs, src_off + len,
				test_buf_size, src_off + len,
				PATTERN_SRC, true);

		pr_debug("%s: verifying dest buffer...\n",
				thread->task->comm);
		error_count += dmatest_verify(thread->dsts, 0, dst_off,
				0, PATTERN_DST, false);
		error_count += dmatest_verify(thread->dsts, dst_off,
				dst_off + len, src_off,
				PATTERN_SRC | PATTERN_COPY, false);
		error_count += dmatest_verify(thread->dsts, dst_off + len,
				test_buf_size, dst_off + len,
				PATTERN_DST, false);

		if (error_count) {
			pr_warning("%s: #%u: %u errors with "
				"src_off=0x%x dst_off=0x%x len=0x%x\n",
				thread_name, total_tests - 1, error_count,
				src_off, dst_off, len);
			failed_tests++;
		} else {
			pr_debug("%s: #%u: No errors with "
				"src_off=0x%x dst_off=0x%x len=0x%x\n",
				thread_name, total_tests - 1,
				src_off, dst_off, len);
		}
	}

	ret = 0;
	for (i = 0; thread->dsts[i]; i++)
		kfree(thread->dsts[i]);
err_dstbuf:
	kfree(thread->dsts);
err_dsts:
	for (i = 0; thread->srcs[i]; i++)
		kfree(thread->srcs[i]);
err_srcbuf:
	kfree(thread->srcs);
err_srcs:
	pr_notice("%s: terminating after %u tests, %u failures (status %d)\n",
			thread_name, total_tests, failed_tests, ret);

	if (iterations > 0)
		while (!kthread_should_stop()) {
			DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wait_dmatest_exit);
			interruptible_sleep_on(&wait_dmatest_exit);
		}

	return ret;
}

6. dmatest_exit():

static void __exit dmatest_exit(void)
{
	struct dmatest_chan *dtc, *_dtc;
	struct dma_chan *chan;

	list_for_each_entry_safe(dtc, _dtc, &dmatest_channels, node) {
		list_del(&dtc->node);
		chan = dtc->chan;
		dmatest_cleanup_channel(dtc);
		pr_debug("dmatest: dropped channel %s\n",
			 dma_chan_name(chan));
		dma_release_channel(chan);
	}
}
module_exit(dmatest_exit);

dmatest_cleanup_channel

static void dmatest_cleanup_channel(struct dmatest_chan *dtc)
{
	struct dmatest_thread	*thread;
	struct dmatest_thread	*_thread;
	int			ret;

	list_for_each_entry_safe(thread, _thread, &dtc->threads, node) {
		ret = kthread_stop(thread->task);
		pr_debug("dmatest: thread %s exited with status %d\n",
				thread->task->comm, ret);
		list_del(&thread->node);
		kfree(thread);
	}
	kfree(dtc);
}