dmaengine: Add core function and capability check for DMA_MEMCPY_SG

This is the old DMA_SG interface that was removed in commit
c678fa66 ("dmaengine: remove DMA_SG as it is dead code in kernel"). It
has been renamed to DMA_MEMCPY_SG to better match the MEMSET and MEMSET_SG
naming convention.

It should only be used for mem2mem copies, either main system memory or
CPU-addressable device memory (like video memory on a PCI graphics card).

Bringing back this interface was prompted by the need to use the Xilinx
CDMA device for mem2mem SG transfers.
Signed-off-by: Adrian Larumbe <adrianml@alumnos.upm.es>
Link: https://lore.kernel.org/r/20211101180825.241048-3-adrianml@alumnos.upm.esSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/dmaengine.c

@@ -1159,6 +1159,13 @@ int dma_async_device_register(struct dma_device *device)
 		return -EIO;
 	}
 
+	if (dma_has_cap(DMA_MEMCPY_SG, device->cap_mask) && !device->device_prep_dma_memcpy_sg) {
+		dev_err(device->dev,
+			"Device claims capability %s, but op is not defined\n",
+			"DMA_MEMCPY_SG");
+		return -EIO;
+	}
+
 	if (dma_has_cap(DMA_XOR, device->cap_mask) && !device->device_prep_dma_xor) {
 		dev_err(device->dev,
 			"Device claims capability %s, but op is not defined\n",

include/linux/dmaengine.h

@@ -50,6 +50,7 @@ enum dma_status {
  */
 enum dma_transaction_type {
 	DMA_MEMCPY,
+	DMA_MEMCPY_SG,
 	DMA_XOR,
 	DMA_PQ,
 	DMA_XOR_VAL,
@@ -891,6 +892,11 @@ struct dma_device {
 	struct dma_async_tx_descriptor *(*device_prep_dma_memcpy)(
 		struct dma_chan *chan, dma_addr_t dst, dma_addr_t src,
 		size_t len, unsigned long flags);
+	struct dma_async_tx_descriptor *(*device_prep_dma_memcpy_sg)(
+		struct dma_chan *chan,
+		struct scatterlist *dst_sg, unsigned int dst_nents,
+		struct scatterlist *src_sg, unsigned int src_nents,
+		unsigned long flags);
 	struct dma_async_tx_descriptor *(*device_prep_dma_xor)(
 		struct dma_chan *chan, dma_addr_t dst, dma_addr_t *src,
 		unsigned int src_cnt, size_t len, unsigned long flags);
@@ -1051,6 +1057,20 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_dma_memcpy(
 						    len, flags);
 }
 
+static inline struct dma_async_tx_descriptor *dmaengine_prep_dma_memcpy_sg(
+		struct dma_chan *chan,
+		struct scatterlist *dst_sg, unsigned int dst_nents,
+		struct scatterlist *src_sg, unsigned int src_nents,
+		unsigned long flags)
+{
+	if (!chan || !chan->device || !chan->device->device_prep_dma_memcpy_sg)
+		return NULL;
+
+	return chan->device->device_prep_dma_memcpy_sg(chan, dst_sg, dst_nents,
+						       src_sg, src_nents,
+						       flags);
+}
+
 static inline bool dmaengine_is_metadata_mode_supported(struct dma_chan *chan,
 		enum dma_desc_metadata_mode mode)
 {