static ssize_t xillyusb_read()

in xillybus/xillyusb.c [1419:1592]

• 106 lines of code
• 29 McCabe index (conditional complexity)

static ssize_t xillyusb_read(struct file *filp, char __user *userbuf,
			     size_t count, loff_t *f_pos)
{
	struct xillyusb_channel *chan = filp->private_data;
	struct xillyusb_dev *xdev = chan->xdev;
	struct xillyfifo *fifo = chan->in_fifo;
	int chan_num = (chan->chan_idx << 1) | 1;

	long deadline, left_to_sleep;
	int bytes_done = 0;
	bool sent_set_push = false;
	int rc;

	deadline = jiffies + 1 + XILLY_RX_TIMEOUT;

	rc = mutex_lock_interruptible(&chan->in_mutex);

	if (rc)
		return rc;

	while (1) {
		u32 fifo_checkpoint_bytes, complete_checkpoint_bytes;
		u32 complete_checkpoint, fifo_checkpoint;
		u32 checkpoint;
		s32 diff, leap;
		unsigned int sh = chan->in_log2_element_size;
		bool checkpoint_for_complete;

		rc = fifo_read(fifo, (__force void *)userbuf + bytes_done,
			       count - bytes_done, xilly_copy_to_user);

		if (rc < 0)
			break;

		bytes_done += rc;
		chan->in_consumed_bytes += rc;

		left_to_sleep = deadline - ((long)jiffies);

		/*
		 * Some 32-bit arithmetic that may wrap. Note that
		 * complete_checkpoint is rounded up to the closest element
		 * boundary, because the read() can't be completed otherwise.
		 * fifo_checkpoint_bytes is rounded down, because it protects
		 * in_fifo from overflowing.
		 */

		fifo_checkpoint_bytes = chan->in_consumed_bytes + fifo->size;
		complete_checkpoint_bytes =
			chan->in_consumed_bytes + count - bytes_done;

		fifo_checkpoint = fifo_checkpoint_bytes >> sh;
		complete_checkpoint =
			(complete_checkpoint_bytes + (1 << sh) - 1) >> sh;

		diff = (fifo_checkpoint - complete_checkpoint) << sh;

		if (chan->in_synchronous && diff >= 0) {
			checkpoint = complete_checkpoint;
			checkpoint_for_complete = true;
		} else {
			checkpoint = fifo_checkpoint;
			checkpoint_for_complete = false;
		}

		leap = (checkpoint - chan->in_current_checkpoint) << sh;

		/*
		 * To prevent flooding of OPCODE_SET_CHECKPOINT commands as
		 * data is consumed, it's issued only if it moves the
		 * checkpoint by at least an 8th of the FIFO's size, or if
		 * it's necessary to complete the number of bytes requested by
		 * the read() call.
		 *
		 * chan->read_data_ok is checked to spare an unnecessary
		 * submission after receiving EOF, however it's harmless if
		 * such slips away.
		 */

		if (chan->read_data_ok &&
		    (leap > (fifo->size >> 3) ||
		     (checkpoint_for_complete && leap > 0))) {
			chan->in_current_checkpoint = checkpoint;
			rc = xillyusb_send_opcode(xdev, chan_num,
						  OPCODE_SET_CHECKPOINT,
						  checkpoint);

			if (rc)
				break;
		}

		if (bytes_done == count ||
		    (left_to_sleep <= 0 && bytes_done))
			break;

		/*
		 * Reaching here means that the FIFO was empty when
		 * fifo_read() returned, but not necessarily right now. Error
		 * and EOF are checked and reported only now, so that no data
		 * that managed its way to the FIFO is lost.
		 */

		if (!READ_ONCE(chan->read_data_ok)) { /* FPGA has sent EOF */
			/* Has data slipped into the FIFO since fifo_read()? */
			smp_rmb();
			if (READ_ONCE(fifo->fill))
				continue;

			rc = 0;
			break;
		}

		if (xdev->error) {
			rc = xdev->error;
			break;
		}

		if (filp->f_flags & O_NONBLOCK) {
			rc = -EAGAIN;
			break;
		}

		if (!sent_set_push) {
			rc = xillyusb_send_opcode(xdev, chan_num,
						  OPCODE_SET_PUSH,
						  complete_checkpoint);

			if (rc)
				break;

			sent_set_push = true;
		}

		if (left_to_sleep > 0) {
			/*
			 * Note that when xdev->error is set (e.g. when the
			 * device is unplugged), read_data_ok turns zero and
			 * fifo->waitq is awaken.
			 * Therefore no special attention to xdev->error.
			 */

			rc = wait_event_interruptible_timeout
				(fifo->waitq,
				 fifo->fill || !chan->read_data_ok,
				 left_to_sleep);
		} else { /* bytes_done == 0 */
			/* Tell FPGA to send anything it has */
			rc = request_read_anything(chan, OPCODE_UPDATE_PUSH);

			if (rc)
				break;

			rc = wait_event_interruptible
				(fifo->waitq,
				 fifo->fill || !chan->read_data_ok);
		}

		if (rc < 0) {
			rc = -EINTR;
			break;
		}
	}

	if (((filp->f_flags & O_NONBLOCK) || chan->poll_used) &&
	    !READ_ONCE(fifo->fill))
		request_read_anything(chan, OPCODE_SET_PUSH);

	mutex_unlock(&chan->in_mutex);

	if (bytes_done)
		return bytes_done;

	return rc;
}