[PATCH v4] dmaengine: xilinx_dma: Support descriptor setup from dma_vecs
From: Folker Schwesinger <hidden>
Date: 2025-08-26 19:01:40
Also in:
dmaengine, lkml
Subsystem:
dma generic offload engine subsystem, the rest · Maintainers:
Vinod Koul, Linus Torvalds
The DMAEngine provides an interface for obtaining DMA transaction
descriptors from an array of scatter gather buffers represented by
struct dma_vec. This interface is used in the DMABUF API of the IIO
framework [1][2].
To enable DMABUF support through the IIO framework for the Xilinx DMA,
implement callback .device_prep_peripheral_dma_vec() of struct
dma_device in the driver.
[1]: 7a86d469983a ("iio: buffer-dmaengine: Support new DMABUF based userspace API")
[2]: 5878853fc938 ("dmaengine: Add API function dmaengine_prep_peripheral_dma_vec()")
Signed-off-by: Folker Schwesinger <redacted>
Reviewed-by: Suraj Gupta <redacted>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
---
Changes in v4:
- Replace external link to relevant source code with commit ids of the
changes introducing dmaengine_prep_peripheral_dma_vec() and the IIO
DMABUF-based API (suggested by Radhey Shyam Pandey).
- Collect R-b tags from v3.
- Link to v3: https://lore.kernel.org/dmaengine/DBZUIRI5Q4A3.1OIBMF9Z5EQ0X@folker-schwesinger.de/ (local)
Changes in v3:
- Collect R-b tags from v2.
- Rebase onto v6.17-rc1.
- Link to v2: https://lore.kernel.org/dmaengine/DAQB7EU7UXR3.Z07Q6JQ1V67Y@folker-schwesinger.de/ (local)
Changes in v2:
- Improve commit message to include reasoning behind the change.
- Rebase onto v6.16-rc1.
- Link to v1: https://lore.kernel.org/dmaengine/D8TV2MP99NTE.1842MMA04VB9N@folker-schwesinger.de/ (local)
---
drivers/dma/xilinx/xilinx_dma.c | 94 +++++++++++++++++++++++++++++++++
1 file changed, 94 insertions(+)
diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index a34d8f0ceed8..fabff602065f 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c@@ -2172,6 +2172,99 @@ xilinx_cdma_prep_memcpy(struct dma_chan *dchan, dma_addr_t dma_dst, return NULL; } +/** + * xilinx_dma_prep_peripheral_dma_vec - prepare descriptors for a DMA_SLAVE + * transaction from DMA vectors + * @dchan: DMA channel + * @vecs: Array of DMA vectors that should be transferred + * @nb: number of entries in @vecs + * @direction: DMA direction + * @flags: transfer ack flags + * + * Return: Async transaction descriptor on success and NULL on failure + */ +static struct dma_async_tx_descriptor *xilinx_dma_prep_peripheral_dma_vec( + struct dma_chan *dchan, const struct dma_vec *vecs, size_t nb, + enum dma_transfer_direction direction, unsigned long flags) +{ + struct xilinx_dma_chan *chan = to_xilinx_chan(dchan); + struct xilinx_dma_tx_descriptor *desc; + struct xilinx_axidma_tx_segment *segment, *head, *prev = NULL; + size_t copy; + size_t sg_used; + unsigned int i; + + if (!is_slave_direction(direction) || direction != chan->direction) + 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; + + /* Build transactions using information from DMA vectors */ + for (i = 0; i < nb; i++) { + sg_used = 0; + + /* Loop until the entire dma_vec entry is used */ + while (sg_used < vecs[i].len) { + struct xilinx_axidma_desc_hw *hw; + + /* Get a free segment */ + segment = xilinx_axidma_alloc_tx_segment(chan); + if (!segment) + goto error; + + /* + * Calculate the maximum number of bytes to transfer, + * making sure it is less than the hw limit + */ + copy = xilinx_dma_calc_copysize(chan, vecs[i].len, + sg_used); + hw = &segment->hw; + + /* Fill in the descriptor */ + xilinx_axidma_buf(chan, hw, vecs[i].addr, sg_used, 0); + hw->control = copy; + + if (prev) + prev->hw.next_desc = segment->phys; + + prev = segment; + sg_used += copy; + + /* + * Insert the segment into the descriptor segments + * list. + */ + list_add_tail(&segment->node, &desc->segments); + } + } + + head = list_first_entry(&desc->segments, struct xilinx_axidma_tx_segment, node); + desc->async_tx.phys = head->phys; + + /* For the last DMA_MEM_TO_DEV transfer, set EOP */ + if (chan->direction == DMA_MEM_TO_DEV) { + segment->hw.control |= XILINX_DMA_BD_SOP; + segment = list_last_entry(&desc->segments, + struct xilinx_axidma_tx_segment, + node); + segment->hw.control |= XILINX_DMA_BD_EOP; + } + + if (chan->xdev->has_axistream_connected) + desc->async_tx.metadata_ops = &xilinx_dma_metadata_ops; + + 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
@@ -3180,6 +3273,7 @@ static int xilinx_dma_probe(struct platform_device *pdev) xdev->common.device_config = xilinx_dma_device_config; if (xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) { dma_cap_set(DMA_CYCLIC, xdev->common.cap_mask); + xdev->common.device_prep_peripheral_dma_vec = xilinx_dma_prep_peripheral_dma_vec; xdev->common.device_prep_slave_sg = xilinx_dma_prep_slave_sg; xdev->common.device_prep_dma_cyclic = xilinx_dma_prep_dma_cyclic;
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585 -- 2.50.1