[PATCH 0/3] dmaengine: Add batched scatter-gather DMA support

[Sumit Kumar <sumit.kumar@oss.qualcomm.com>]

Synopsys DesignWare eDMA IP supports a linked-list (LL) mode where
each LL item carries independent source and destination addresses. This
allows multiple independent memory transfers to be described in a single
linked list and submitted to the hardware as one DMA transaction, without
any CPU intervention between items. The IP processes LL items strictly
in order, guaranteeing that scatter-gather entries are never reordered.

This series leverages that hardware capability to introduce a new
dmaengine API — dmaengine_prep_batch_sg_dma() — for batching multiple
independent buffers into a single DMA transaction. Each scatter-gather
entry specifies both its own source (dma_address) and destination
(dma_dst_address), enabling the eDMA hardware to process them as a
single linked-list transaction.

The primary use case is MHI endpoint ring caching. When an MHI ring
wraps around, data spans two non-contiguous memory regions (tail and
head portions). Previously this required two separate DMA transactions
with two interrupts. With this series, both regions are submitted as a
single batched transaction, reducing submission overhead and interrupt
count.

The series includes:
1. Core DMA engine API and DW eDMA driver implementation
2. PCI EPF MHI driver support for batched transfers
3. MHI endpoint ring caching optimization using batched reads

Performance Benefits:
--------------------
- Reduced DMA submission overhead for multiple transfers
- Better hardware utilization through batched operations
- Lower latency for ring wraparound scenarios

Signed-off-by: Sumit Kumar <sumit.kumar@oss.qualcomm.com>
---
Sumit Kumar (3):
      dmaengine: Add multi-buffer support in single DMA transfer
      PCI: epf-mhi: Add batched DMA read support
      bus: mhi: ep: Use batched read for ring caching

 drivers/bus/mhi/ep/ring.c                    |  43 +++++-----
 drivers/dma/dw-edma/Kconfig                  |   1 +
 drivers/dma/dw-edma/dw-edma-core.c           |  40 ++++++++-
 drivers/dma/dw-edma/dw-edma-core.h           |   3 +-
 drivers/pci/endpoint/functions/Kconfig       |   1 +
 drivers/pci/endpoint/functions/pci-epf-mhi.c | 120 +++++++++++++++++++++++++++
 include/linux/dmaengine.h                    |  29 ++++++-
 include/linux/mhi_ep.h                       |   3 +
 include/linux/scatterlist.h                  |   7 ++
 kernel/dma/Kconfig                           |   3 +
 10 files changed, 224 insertions(+), 26 deletions(-)
---
base-commit: f0b9d8eb98dfee8d00419aa07543bdc2c1a44fb1
change-id: 20260108-dma_multi_sg-c217650373c2

Best regards,
-- 
Sumit Kumar <sumit.kumar@oss.qualcomm.com>