linux/drivers/dma/dmaengine.h

/*
 * The contents of this file are private to DMA engine drivers, and is not
 * part of the API to be used by DMA engine users.
 */
#ifndef DMAENGINE_H
#define DMAENGINE_H

#include <linux/dmaengine.h>

/**
 * dma_cookie_assign - assign a DMA engine cookie to the descriptor
 * @tx: descriptor needing cookie
 *
 * Assign a unique non-zero per-channel cookie to the descriptor.
 * Note: caller is expected to hold a lock to prevent concurrency.
 */
static inline dma_cookie_t dma_cookie_assign(struct dma_async_tx_descriptor *tx)
{
	struct dma_chan *chan = tx->chan;
	dma_cookie_t cookie;

	cookie = chan->cookie + 1;
	if (cookie < DMA_MIN_COOKIE)
		cookie = DMA_MIN_COOKIE;
	tx->cookie = chan->cookie = cookie;

	return cookie;
}

#endif