dmaengine: introduce common linked-list DMA controller framework

Many DMA engines, such as fsl-edma, at-hdmac, and ste-dma40, use
linked-list descriptors for data transfers and share a large amount of
common logic.

Introduce a basic framework for linked-list–based DMA controllers as a
first step toward a common library.

All DMA descriptors have a uniform size and are chained as follows:

    ┌──────┐    ┌──────┐    ┌──────┐
    │      │ ┌─►│      │ ┌─►│      │
    │      │ │  │      │ │  │      │
    ├──────┤ │  ├──────┤ │  ├──────┤
    │ Next ├─┘  │ Next ├─┘  │ Next │
    └──────┘    └──────┘    └──────┘

The framework is derived from the fsl-edma implementation and provides
common descriptor allocation/free and helpers for prep_memcpy(),
prep_slave_sg(), and prep_slave_cyclic().

This patch series is based on:
  https://lore.kernel.org/dmaengine/20260114-dma_common_con...

Additional functionality can be added if everyone agree on this method.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
Frank Li (12):
      dmaengine: Extend virt_chan for link list based DMA engines
      dmaengine: Add common dma_ll_desc and dma_linklist_item for link-list controllers
      dmaengine: fsl-edma: Remove redundant echan from struct fsl_edma_desc
      dmaengine: fsl-edma: Use common dma_ll_desc in vchan
      dmaengine: Add DMA pool allocation in vchan_dma_ll_init() and API vchan_dma_ll_free()
      dmaengine: Move fsl_edma_(alloc|free)_desc() to common library
      dmaengine: virt-dma: split vchan_tx_prep() into init and internal helpers
      dmaengine: Factor out fsl-edma prep_memcpy into common vchan helper
      dmaengine: ll-dma: support multi-descriptor memcpy for large transfers
      dmaengine: move fsl-edma dma_[un]map_resource() to linked list library
      dmaengine: fsl-edma: use local soff/doff variables
      dmaengine: add vchan_dma_ll_prep_slave_{sg,cyclic} API

 drivers/dma/Kconfig           |   4 +
 drivers/dma/Makefile          |   1 +
 drivers/dma/fsl-edma-common.c | 448 +++++++++++++-----------------------------
 drivers/dma/fsl-edma-common.h |  35 +---
 drivers/dma/fsl-edma-main.c   |   8 +-
 drivers/dma/ll-dma.c          | 353 +++++++++++++++++++++++++++++++++
 drivers/dma/mcf-edma-main.c   |   6 +-
 drivers/dma/virt-dma.h        | 114 +++++++++--
 8 files changed, 606 insertions(+), 363 deletions(-)
---
base-commit: daf496ddce1475078b500e30e0a16de3d8fb9c8a
change-id: 20260119-dma_ll_comlib-ba69c554917d

Best regards,
--
Frank Li <Frank.Li@nxp.com>