[PATCH v8 0/2] dmaengine: fsl-edma: Scatter/gather improvements

This series adds support for scatter/gather DMA transfers via dma_vec
and dynamic descriptor chaining to the Freescale eDMA controller driver.

The first patch implements the .device_prep_peripheral_dma_vec() callback,
enabling the DMA engine to accept an array of dma_vec structures. This
callback supports both regular and cyclic transfer modes.

The second patch introduces dynamic scatter/gather chaining, which allows
multiple DMA descriptors to be linked together without stopping the channel.
This optimization eliminates idle periods when back-to-back transfers are
submitted, improving throughput and reducing latency. The implementation
carefully preserves cyclic transfer semantics and respects hardware
constraints on platforms with split register layouts.

I tested it on the i.MX93. The dynamic scatter/gather chaining should
work with other eDMA controller with split register layout.

Signed-off-by: Benoît Monin <[email protected]>
---
Changes in v8:
- Enforce that major channel linking in not used when linking a descriptor
  in fsl_edma_link_sg() by checking all TCD, not just the first one.
- Don't compare the descriptor link_sg_id with the CSR LINKCH field
  if major channel linking is enabled, to avoid completing unfinished
  descriptors in fsl_edma_tx_chan_handler().
- Handle the completion of the last transaction of a linked SG chain if
  the previous interrupt was missed by checking for the channel completion.
- Add comments to clarify the assumptions I made.
- Link to v7: https://patch.msgid.link/[email protected]

Changes in v7:
- In fsl_edma_prep_peripheral_dma_vec(), make sure that CITER/BITER
  values fit in their registers.
- Add the identifier to all TCD of a linked transaction so that we can
  always identify it when handling the end-of-transfer interrupt.
- Handle missed/coalesced end-of-transfer interrupt even when the transfer
  is completed.
- Link to v6: https://patch.msgid.link/[email protected]

Changes in v6:
- Link DMA transactions in fsl_edma_issue_pending() when they are issued,
  not when submitted.
- Add an identifier to linked transactions to handle missed/coalesced
  end-of-transfer interrupt.
- Link to v5: https://patch.msgid.link/[email protected]

Changes in v5:
- Rebased on v7.2-rc1.
- Add a call to dma_wmb() to ensure that dlast_sga is updated
  before csr when linking scatter/gather transactions.
- Don't update TCD registers if updating csr requires clearing the
  channel DONE bit to avoid a status mismatch in fsl_edma_tx_chan_handler().
- Link to v4: https://patch.msgid.link/[email protected]

Changes in v4:
- To keep transactions in order, link DMA transaction to the end of
  submitted list first, only lookup the issued list is the submitted
  list is empty.
- Link to v3: https://patch.msgid.link/[email protected]

Changes in v3:
- Fix formatting errors reported by Frank Li.
- Add fsl_edma_tx_submit() to link the DMA transactions
  when they are submitted, not when they are prepared.
- Link to v2: https://patch.msgid.link/[email protected]

Changes in v2:
- Drop the RFC prefix, as asked by Frank Li
- No code change
- Link to v1: https://patch.msgid.link/[email protected]

To: Frank Li <[email protected]>
To: Vinod Koul <[email protected]>
Cc: Thomas Petazzoni <[email protected]>
Cc: Frank Li <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]

---
Benoît Monin (2):
      dmaengine: fsl-edma: Implement device_prep_peripheral_dma_vec
      dmaengine: fsl-edma: Support dynamic scatter/gather chaining

 drivers/dma/fsl-edma-common.c | 241 ++++++++++++++++++++++++++++++++++++++++--
 drivers/dma/fsl-edma-common.h |   7 ++
 drivers/dma/fsl-edma-main.c   |   2 +
 drivers/dma/fsl-edma-trace.h  |   5 +
 4 files changed, 248 insertions(+), 7 deletions(-)
---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260428-fsl-edma-dyn-sg-960731e37da2

Best regards,
--  
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com