Re: [PATCH] dmaengine: Remove DMA_MEMCPY_SG operation as it has no consumers

Vinod Koul
2022-07-26T12:28:00Z

On 26-07-22, 10:43, Adrian Larumbe wrote:
> There are no in kernel consumers for DMA_MEMCPY_SG. Remove operation and
> Xilinx CDMA driver code which implemented it.

What was this based on?
>
> This reverts the following commits:

Did you see 0cae04373b77 ("dmaengine: remove DMA_MEMCPY_SG once again")

>
> - commit 58fe10766048 ("dmaengine: Add documentation for new memcpy
> scatter-gather function")
> - commit 3218910fd585 ("dmaengine: Add core function and capability check
> for DMA_MEMCPY_SG")
> - commit 29cf37fa6dd9 ("dmaengine: Add consumer for the new DMA_MEMCPY_SG
> API function.")
>
> Signed-off-by: Adrian Larumbe <adrian.larumbe@collabora.com>
> ---
> .../driver-api/dmaengine/provider.rst | 23 ----
> drivers/dma/dmaengine.c | 7 -
> drivers/dma/xilinx/xilinx_dma.c | 122 ------------------
> include/linux/dmaengine.h | 20 ---
> 4 files changed, 172 deletions(-)
>
> diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst
> index 1e0f1f85d10e..8cf704332bb4 100644
> --- a/Documentation/driver-api/dmaengine/provider.rst
> +++ b/Documentation/driver-api/dmaengine/provider.rst
> @@ -162,29 +162,6 @@ Currently, the types available are:
>
> - 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
> - both lists need not be the same, and that the operation functionally is
> - equivalent to a ``strncpy`` where the ``count`` argument equals the smallest
> - total size of the two scatter-gather list buffers.
> -
> - - It's usually used for copying pixel data between host memory and
> - memory-mapped GPU device memory, such as found on modern PCI video graphics
> - cards. The most immediate example is the OpenGL API function
> - ``glReadPielx()``, which might require a verbatim copy of a huge framebuffer
> - from local device memory onto host memory.
> -
> - DMA_XOR
>
> - The device is able to perform XOR operations on memory areas
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index e80feeea0e01..c741b6431958 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -1153,13 +1153,6 @@ 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",
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index cd62bbb50e8b..6276934d4d2b 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -2127,126 +2127,6 @@ xilinx_cdma_prep_memcpy(struct dma_chan *dchan, dma_addr_t dma_dst,
> return NULL;
> }
>
> -/**
> - * 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
> @@ -3240,9 +3120,7 @@ static int xilinx_dma_probe(struct platform_device *pdev)
> 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;
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index b46b88e6aa0d..c923f4e60f24 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -50,7 +50,6 @@ enum dma_status {
> */
> enum dma_transaction_type {
> DMA_MEMCPY,
> - DMA_MEMCPY_SG,
> DMA_XOR,
> DMA_PQ,
> DMA_XOR_VAL,
> @@ -887,11 +886,6 @@ 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);
> @@ -1060,20 +1054,6 @@ 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)
> {
> --
> 2.37.0

--
~Vinod