dmaengine: dma-jz4780: Use 4-word descriptors

The only information we use in the 8-word version of the hardware DMA
descriptor that is not present in the 4-word version is the transfer
type, aka. the ID of the source or recipient device.

Since the transfer type will never change for a DMA channel in use,
we can just set it once for all in the corresponding DMA register
before starting any transfer.

This has several benefits:

* the driver will handle twice as many hardware DMA descriptors;

* the driver is closer to support the JZ4740, which only supports 4-word
  hardware DMA descriptors;

* the JZ4770 SoC needs the transfer type to be set in the corresponding
  DMA register anyway, even if 8-word descriptors are in use.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: Mathieu Malaterre <malat@debian.org>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/dma-jz4780.c

@@ -95,17 +95,12 @@
  * @dtc: transfer count (number of blocks of the transfer size specified in DCM
  * to transfer) in the low 24 bits, offset of the next descriptor from the
  * descriptor base address in the upper 8 bits.
- * @sd: target/source stride difference (in stride transfer mode).
- * @drt: request type
  */
 struct jz4780_dma_hwdesc {
 	uint32_t dcm;
 	uint32_t dsa;
 	uint32_t dta;
 	uint32_t dtc;
-	uint32_t sd;
-	uint32_t drt;
-	uint32_t reserved[2];
 };
 
 /* Size of allocations for hardware descriptor blocks. */
@@ -281,7 +276,6 @@ static int jz4780_dma_setup_hwdesc(struct jz4780_dma_chan *jzchan,
 		desc->dcm = JZ_DMA_DCM_SAI;
 		desc->dsa = addr;
 		desc->dta = config->dst_addr;
-		desc->drt = jzchan->transfer_type;
 
 		width = config->dst_addr_width;
 		maxburst = config->dst_maxburst;
@@ -289,7 +283,6 @@ static int jz4780_dma_setup_hwdesc(struct jz4780_dma_chan *jzchan,
 		desc->dcm = JZ_DMA_DCM_DAI;
 		desc->dsa = config->src_addr;
 		desc->dta = addr;
-		desc->drt = jzchan->transfer_type;
 
 		width = config->src_addr_width;
 		maxburst = config->src_maxburst;
@@ -434,9 +427,10 @@ static struct dma_async_tx_descriptor *jz4780_dma_prep_dma_memcpy(
 	tsz = jz4780_dma_transfer_size(dest | src | len,
 				       &jzchan->transfer_shift);
 
+	jzchan->transfer_type = JZ_DMA_DRT_AUTO;
+
 	desc->desc[0].dsa = src;
 	desc->desc[0].dta = dest;
-	desc->desc[0].drt = JZ_DMA_DRT_AUTO;
 	desc->desc[0].dcm = JZ_DMA_DCM_TIE | JZ_DMA_DCM_SAI | JZ_DMA_DCM_DAI |
 			    tsz << JZ_DMA_DCM_TSZ_SHIFT |
 			    JZ_DMA_WIDTH_32_BIT << JZ_DMA_DCM_SP_SHIFT |
@@ -491,9 +485,12 @@ static void jz4780_dma_begin(struct jz4780_dma_chan *jzchan)
 			(jzchan->curr_hwdesc + 1) % jzchan->desc->count;
 	}
 
-	/* Use 8-word descriptors. */
-	jz4780_dma_chn_writel(jzdma, jzchan->id,
-			      JZ_DMA_REG_DCS, JZ_DMA_DCS_DES8);
+	/* Use 4-word descriptors. */
+	jz4780_dma_chn_writel(jzdma, jzchan->id, JZ_DMA_REG_DCS, 0);
+
+	/* Set transfer type. */
+	jz4780_dma_chn_writel(jzdma, jzchan->id, JZ_DMA_REG_DRT,
+			      jzchan->transfer_type);
 
 	/* Write descriptor address and initiate descriptor fetch. */
 	desc_phys = jzchan->desc->desc_phys +
@@ -503,7 +500,7 @@ static void jz4780_dma_begin(struct jz4780_dma_chan *jzchan)
 
 	/* Enable the channel. */
 	jz4780_dma_chn_writel(jzdma, jzchan->id, JZ_DMA_REG_DCS,
-			      JZ_DMA_DCS_DES8 | JZ_DMA_DCS_CTE);
+			      JZ_DMA_DCS_CTE);
 }
 
 static void jz4780_dma_issue_pending(struct dma_chan *chan)