DMA to and from GPMC using dmaengine

I'm trying to do DMA to and from GPMC in linux. This will work if I use a MEM_TO_MEM transaction through device_prep_dma_memcpy(). The caveat is that the dma driver will set the transaction to 32-bit bursts, which limits the GPMC bursts to 2x16bit. I've been trying to use dmaengine_prep_slave_single(), but I can't figure out how to get the transfer working. The transfer never starts after I issue dma_async_issue_pending();

I've tried quite a number of combinations, but I just can't figure out what it is that I'm missing. How can I get this running properly?

Code looks something like:

static void dma_callback(void *param)
{
	complete(&dma_comp);
}

	int ch_num = 52;
	dma_buf = dma_alloc_coherent(NULL, MAX_DMA_TRANSFER_IN_BYTES,
					      &dma_phys_addr, GFP_KERNEL);
	dma_cap_zero(mask);
	dma_cap_set(DMA_SLAVE, mask);
	dma_chan = dma_request_channel(mask, edma_filter_fn, &ch_num);

int my_dma_copy(struct my_dev_class* my_dev, dma_addr_t dest_addr,
		  dma_addr_t src_addr, int count, bool is_write)
{
	unsigned int ch_num = 52;

	dir = is_write ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
	dma_addr_t mem_dma_addr = is_write ? src_addr : dest_addr;

	struct dma_slave_config	conf = {
		.src_addr = src_addr,
		.dst_addr = dest_addr,
		.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES,
		.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES,
		.src_maxburst = 16,
		.dst_maxburst = 16,
		.device_fc = 0,
		.slave_id = 0,
	};
	
	result = dmaengine_slave_config(chan, &conf);

	/* This works, but does not do GPMC bursts */
	tx = dma_chan->device->device_prep_dma_memcpy(chan, trgt_addr, src_addr,
							count, 
							DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
	/* This doesn't trigger any data over GPMC */
	//tx = dmaengine_prep_slave_single(dma_chan, mem_dma_addr, count, dir, 
	//					DMA_CTRL_ACK | DMA_PREP_INTERRUPT); 
	reinit_competion(&dma_comp);

	tx->callback = dma_callback;
	cookie = dmaengine_submit(tx);

	dma_async_issue_pending(chan);
	wait_for_completion(&dma_comp);
}

	dma_release_channel(dma_chan);
	dma_free_coherent(NULL, MAX_DMA_TRANSFER_IN_BYTES, dma_buf, dma_phys_addr);