dmaengine: xdmac: Add scatter gathered memset support

The XDMAC also supports memset operations over discontiguous areas. Add the
necessary logic to support this.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/at_xdmac.c

@@ -1133,7 +1133,7 @@ static struct at_xdmac_desc *at_xdmac_memset_create_desc(struct dma_chan *chan,
 	 * SAMA5D4x), so we can use the same interface for source and dest,
 	 * that solves the fact we don't know the direction.
 	 */
-	u32			chan_cc = AT_XDMAC_CC_DAM_INCREMENTED_AM
+	u32			chan_cc = AT_XDMAC_CC_DAM_UBS_AM
 					| AT_XDMAC_CC_SAM_INCREMENTED_AM
 					| AT_XDMAC_CC_DIF(0)
 					| AT_XDMAC_CC_SIF(0)
@@ -1201,6 +1201,168 @@ at_xdmac_prep_dma_memset(struct dma_chan *chan, dma_addr_t dest, int value,
 	return &desc->tx_dma_desc;
 }
 
+static struct dma_async_tx_descriptor *
+at_xdmac_prep_dma_memset_sg(struct dma_chan *chan, struct scatterlist *sgl,
+			    unsigned int sg_len, int value,
+			    unsigned long flags)
+{
+	struct at_xdmac_chan	*atchan = to_at_xdmac_chan(chan);
+	struct at_xdmac_desc	*desc, *pdesc = NULL,
+				*ppdesc = NULL, *first = NULL;
+	struct scatterlist	*sg, *psg = NULL, *ppsg = NULL;
+	size_t			stride = 0, pstride = 0, len = 0;
+	int			i;
+
+	if (!sgl)
+		return NULL;
+
+	dev_dbg(chan2dev(chan), "%s: sg_len=%d, value=0x%x, flags=0x%lx\n",
+		__func__, sg_len, value, flags);
+
+	/* Prepare descriptors. */
+	for_each_sg(sgl, sg, sg_len, i) {
+		dev_dbg(chan2dev(chan), "%s: dest=0x%08x, len=%d, pattern=0x%x, flags=0x%lx\n",
+			__func__, sg_dma_address(sg), sg_dma_len(sg),
+			value, flags);
+		desc = at_xdmac_memset_create_desc(chan, atchan,
+						   sg_dma_address(sg),
+						   sg_dma_len(sg),
+						   value);
+		if (!desc && first)
+			list_splice_init(&first->descs_list,
+					 &atchan->free_descs_list);
+
+		if (!first)
+			first = desc;
+
+		/* Update our strides */
+		pstride = stride;
+		if (psg)
+			stride = sg_dma_address(sg) -
+				(sg_dma_address(psg) + sg_dma_len(psg));
+
+		/*
+		 * The scatterlist API gives us only the address and
+		 * length of each elements.
+		 *
+		 * Unfortunately, we don't have the stride, which we
+		 * will need to compute.
+		 *
+		 * That make us end up in a situation like this one:
+		 *    len    stride    len    stride    len
+		 * +-------+        +-------+        +-------+
+		 * |  N-2  |        |  N-1  |        |   N   |
+		 * +-------+        +-------+        +-------+
+		 *
+		 * We need all these three elements (N-2, N-1 and N)
+		 * to actually take the decision on whether we need to
+		 * queue N-1 or reuse N-2.
+		 *
+		 * We will only consider N if it is the last element.
+		 */
+		if (ppdesc && pdesc) {
+			if ((stride == pstride) &&
+			    (sg_dma_len(ppsg) == sg_dma_len(psg))) {
+				dev_dbg(chan2dev(chan),
+					"%s: desc 0x%p can be merged with desc 0x%p\n",
+					__func__, pdesc, ppdesc);
+
+				/*
+				 * Increment the block count of the
+				 * N-2 descriptor
+				 */
+				at_xdmac_increment_block_count(chan, ppdesc);
+				ppdesc->lld.mbr_dus = stride;
+
+				/*
+				 * Put back the N-1 descriptor in the
+				 * free descriptor list
+				 */
+				list_add_tail(&pdesc->desc_node,
+					      &atchan->free_descs_list);
+
+				/*
+				 * Make our N-1 descriptor pointer
+				 * point to the N-2 since they were
+				 * actually merged.
+				 */
+				pdesc = ppdesc;
+
+			/*
+			 * Rule out the case where we don't have
+			 * pstride computed yet (our second sg
+			 * element)
+			 *
+			 * We also want to catch the case where there
+			 * would be a negative stride,
+			 */
+			} else if (pstride ||
+				   sg_dma_address(sg) < sg_dma_address(psg)) {
+				/*
+				 * Queue the N-1 descriptor after the
+				 * N-2
+				 */
+				at_xdmac_queue_desc(chan, ppdesc, pdesc);
+
+				/*
+				 * Add the N-1 descriptor to the list
+				 * of the descriptors used for this
+				 * transfer
+				 */
+				list_add_tail(&desc->desc_node,
+					      &first->descs_list);
+				dev_dbg(chan2dev(chan),
+					"%s: add desc 0x%p to descs_list 0x%p\n",
+					__func__, desc, first);
+			}
+		}
+
+		/*
+		 * If we are the last element, just see if we have the
+		 * same size than the previous element.
+		 *
+		 * If so, we can merge it with the previous descriptor
+		 * since we don't care about the stride anymore.
+		 */
+		if ((i == (sg_len - 1)) &&
+		    sg_dma_len(ppsg) == sg_dma_len(psg)) {
+			dev_dbg(chan2dev(chan),
+				"%s: desc 0x%p can be merged with desc 0x%p\n",
+				__func__, desc, pdesc);
+
+			/*
+			 * Increment the block count of the N-1
+			 * descriptor
+			 */
+			at_xdmac_increment_block_count(chan, pdesc);
+			pdesc->lld.mbr_dus = stride;
+
+			/*
+			 * Put back the N descriptor in the free
+			 * descriptor list
+			 */
+			list_add_tail(&desc->desc_node,
+				      &atchan->free_descs_list);
+		}
+
+		/* Update our descriptors */
+		ppdesc = pdesc;
+		pdesc = desc;
+
+		/* Update our scatter pointers */
+		ppsg = psg;
+		psg = sg;
+
+		len += sg_dma_len(sg);
+	}
+
+	first->tx_dma_desc.cookie = -EBUSY;
+	first->tx_dma_desc.flags = flags;
+	first->xfer_size = len;
+
+	return &first->tx_dma_desc;
+}
+
 static enum dma_status
 at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
 		struct dma_tx_state *txstate)
@@ -1734,6 +1896,7 @@ static int at_xdmac_probe(struct platform_device *pdev)
 	dma_cap_set(DMA_INTERLEAVE, atxdmac->dma.cap_mask);
 	dma_cap_set(DMA_MEMCPY, atxdmac->dma.cap_mask);
 	dma_cap_set(DMA_MEMSET, atxdmac->dma.cap_mask);
+	dma_cap_set(DMA_MEMSET_SG, atxdmac->dma.cap_mask);
 	dma_cap_set(DMA_SLAVE, atxdmac->dma.cap_mask);
 	/*
 	 * Without DMA_PRIVATE the driver is not able to allocate more than
@@ -1749,6 +1912,7 @@ static int at_xdmac_probe(struct platform_device *pdev)
 	atxdmac->dma.device_prep_interleaved_dma	= at_xdmac_prep_interleaved;
 	atxdmac->dma.device_prep_dma_memcpy		= at_xdmac_prep_dma_memcpy;
 	atxdmac->dma.device_prep_dma_memset		= at_xdmac_prep_dma_memset;
+	atxdmac->dma.device_prep_dma_memset_sg		= at_xdmac_prep_dma_memset_sg;
 	atxdmac->dma.device_prep_slave_sg		= at_xdmac_prep_slave_sg;
 	atxdmac->dma.device_config			= at_xdmac_device_config;
 	atxdmac->dma.device_pause			= at_xdmac_device_pause;