dmaengine: remove DMA_MEMCPY_SG once again

This was removed before due to the complete lack of users, but
3218910fd585 ("dmaengine: Add core function and capability check for
DMA_MEMCPY_SG") and 29cf37fa6dd9 ("dmaengine: Add consumer for the new
DMA_MEMCPY_SG API function.") added it back despite still not having
any users whatsoever.

Fixes: 3218910fd585 ("dmaengine: Add core function and capability check for DMA_MEMCPY_SG")
Fixes: 29cf37fa6dd9 ("dmaengine: Add consumer for the new DMA_MEMCPY_SG API function.")
Signed-off-by: Christoph Hellwig <[e-mail]>
Acked-by: Michal Simek <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/driver-api/dmaengine/provider.rst

···
 
   - The device is able to do memory to memory copies
 
-- - DMA_MEMCPY_SG
-
-  - The device supports memory to memory scatter-gather transfers.
-
-  - Even though a plain memcpy can look like a particular case of a
-    scatter-gather transfer, with a single chunk to copy, it's a distinct
-    transaction type in the mem2mem transfer case. This is because some very
-    simple devices might be able to do contiguous single-chunk memory copies,
-    but have no support for more complex SG transfers.
-
   - No matter what the overall size of the combined chunks for source and
     destination is, only as many bytes as the smallest of the two will be
     transmitted. That means the number and size of the scatter-gather buffers in

drivers/dma/dmaengine.c

···
 		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",

drivers/dma/xilinx/xilinx_dma.c

···
 }
 
 /**
- * xilinx_cdma_prep_memcpy_sg - prepare descriptors for a memcpy_sg transaction
- * @dchan: DMA channel
- * @dst_sg: Destination scatter list
- * @dst_sg_len: Number of entries in destination scatter list
- * @src_sg: Source scatter list
- * @src_sg_len: Number of entries in source scatter list
- * @flags: transfer ack flags
- *
- * Return: Async transaction descriptor on success and NULL on failure
- */
-static struct dma_async_tx_descriptor *xilinx_cdma_prep_memcpy_sg(
-			struct dma_chan *dchan, struct scatterlist *dst_sg,
-			unsigned int dst_sg_len, struct scatterlist *src_sg,
-			unsigned int src_sg_len, unsigned long flags)
-{
-	struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
-	struct xilinx_dma_tx_descriptor *desc;
-	struct xilinx_cdma_tx_segment *segment, *prev = NULL;
-	struct xilinx_cdma_desc_hw *hw;
-	size_t len, dst_avail, src_avail;
-	dma_addr_t dma_dst, dma_src;
-
-	if (unlikely(dst_sg_len == 0 || src_sg_len == 0))
-		return NULL;
-
-	if (unlikely(!dst_sg  || !src_sg))
-		return NULL;
-
-	desc = xilinx_dma_alloc_tx_descriptor(chan);
-	if (!desc)
-		return NULL;
-
-	dma_async_tx_descriptor_init(&desc->async_tx, &chan->common);
-	desc->async_tx.tx_submit = xilinx_dma_tx_submit;
-
-	dst_avail = sg_dma_len(dst_sg);
-	src_avail = sg_dma_len(src_sg);
-	/*
-	 * loop until there is either no more source or no more destination
-	 * scatterlist entry
-	 */
-	while (true) {
-		len = min_t(size_t, src_avail, dst_avail);
-		len = min_t(size_t, len, chan->xdev->max_buffer_len);
-		if (len == 0)
-			goto fetch;
-
-		/* Allocate the link descriptor from DMA pool */
-		segment = xilinx_cdma_alloc_tx_segment(chan);
-		if (!segment)
-			goto error;
-
-		dma_dst = sg_dma_address(dst_sg) + sg_dma_len(dst_sg) -
-			dst_avail;
-		dma_src = sg_dma_address(src_sg) + sg_dma_len(src_sg) -
-			src_avail;
-		hw = &segment->hw;
-		hw->control = len;
-		hw->src_addr = dma_src;
-		hw->dest_addr = dma_dst;
-		if (chan->ext_addr) {
-			hw->src_addr_msb = upper_32_bits(dma_src);
-			hw->dest_addr_msb = upper_32_bits(dma_dst);
-		}
-
-		if (prev) {
-			prev->hw.next_desc = segment->phys;
-			if (chan->ext_addr)
-				prev->hw.next_desc_msb =
-					upper_32_bits(segment->phys);
-		}
-
-		prev = segment;
-		dst_avail -= len;
-		src_avail -= len;
-		list_add_tail(&segment->node, &desc->segments);
-
-fetch:
-		/* Fetch the next dst scatterlist entry */
-		if (dst_avail == 0) {
-			if (dst_sg_len == 0)
-				break;
-			dst_sg = sg_next(dst_sg);
-			if (dst_sg == NULL)
-				break;
-			dst_sg_len--;
-			dst_avail = sg_dma_len(dst_sg);
-		}
-		/* Fetch the next src scatterlist entry */
-		if (src_avail == 0) {
-			if (src_sg_len == 0)
-				break;
-			src_sg = sg_next(src_sg);
-			if (src_sg == NULL)
-				break;
-			src_sg_len--;
-			src_avail = sg_dma_len(src_sg);
-		}
-	}
-
-	if (list_empty(&desc->segments)) {
-		dev_err(chan->xdev->dev,
-			"%s: Zero-size SG transfer requested\n", __func__);
-		goto error;
-	}
-
-	/* Link the last hardware descriptor with the first. */
-	segment = list_first_entry(&desc->segments,
-				struct xilinx_cdma_tx_segment, node);
-	desc->async_tx.phys = segment->phys;
-	prev->hw.next_desc = segment->phys;
-
-	return &desc->async_tx;
-
-error:
-	xilinx_dma_free_tx_descriptor(chan, desc);
-	return NULL;
-}
-
-/**
  * xilinx_dma_prep_slave_sg - prepare descriptors for a DMA_SLAVE transaction
  * @dchan: DMA channel
  * @sgl: scatterlist to transfer to/from
···
 					  DMA_RESIDUE_GRANULARITY_SEGMENT;
 	} else if (xdev->dma_config->dmatype == XDMA_TYPE_CDMA) {
 		dma_cap_set(DMA_MEMCPY, xdev->common.cap_mask);
-		dma_cap_set(DMA_MEMCPY_SG, xdev->common.cap_mask);
 		xdev->common.device_prep_dma_memcpy = xilinx_cdma_prep_memcpy;
-		xdev->common.device_prep_dma_memcpy_sg = xilinx_cdma_prep_memcpy_sg;
 		/* Residue calculation is supported by only AXI DMA and CDMA */
 		xdev->common.residue_granularity =
 					  DMA_RESIDUE_GRANULARITY_SEGMENT;

include/linux/dmaengine.h

···
  */
 enum dma_transaction_type {
 	DMA_MEMCPY,
-	DMA_MEMCPY_SG,
 	DMA_XOR,
 	DMA_PQ,
 	DMA_XOR_VAL,
···
 	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);
···
 
 	return chan->device->device_prep_dma_memcpy(chan, dest, src,
 						    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,