On Wed, Oct 10, 2012 at 03:43:07PM +0200, ludovic.desroches at atmel.com wrote:

+	txdesc = chan_tx->device->device_prep_slave_sg(chan_tx, &dma->sg,
+		1, DMA_TO_DEVICE, DMA_PREP_INTERRUPT | DMA_CTRL_ACK, NULL);

No, a while back the DMA engine API changed.  It no longer takes
DMA_TO_DEVICE/DMA_FROM_DEVICE but DMA_MEM_TO_DEV and DMA_DEV_TO_MEM.

+	/* Keep in mind that we won't use dma to read the last two bytes */
+	at91_twi_irq_save(dev);
+	dma_addr = dma_map_single(dev->dev, dev->buf, dev->buf_len - 2,
+				  DMA_FROM_DEVICE);

Ditto.

+	dma->xfer_in_progress = true;
+	cookie = rxdesc->tx_submit(rxdesc);
+	if (dma_submit_error(cookie)) {

tx_submit never errors (anymore.)

+	slave_config.direction = DMA_TO_DEVICE;

Same comment as for the other directions.  Note that DMA engine drivers
really should ignore this parameter now, and DMA engine users should phase
it out.

+	if (dmaengine_slave_config(dma->chan_tx, &slave_config)) {
+		dev_err(dev->dev, "failed to configure tx channel\n");
+		ret = -EINVAL;
+		goto error;
+	}
+
+	slave_config.direction = DMA_FROM_DEVICE;

Ditto.