[PATCH v6 00/10] dmaengine: dw-edma: Prepare for dynamic LL appends

[Koichiro Den]

Hi,

This is the first 10 patches from v5, split out following Frank's
suggestion:
https://lore.kernel.org/r/anzgNmxSV2vf1w1X@lizhi-Precision-Tower-5810/

This prep series converts the LL into a reusable circular ring and
prepares the doorbell and IRQ paths for the follow-up series,
"Support dynamic LL appends".

This series is based on dmaengine/next.


Notes
=====

- One temporary limitation caused by this split is that a descriptor must
  fit in the usable ring. Patch 4 rejects descriptors that exceed it, and
  the follow-up removes this limit once LL progress reclamation is added.
  See:
  https://lore.kernel.org/all/a62w2vkektwuksvz4oqkozqu27knzsqdroj7xprfm47twz5cs7@rd42oqapg5z2/
  Frank and I agreed off-list that this restriction is acceptable because
  a single descriptor with roughly 170 or more elements is unusual.

- Although this series does not append requests while a channel is
  running, it can still reduce per-transfer overhead by reusing the
  circular LL context: the driver no longer rewrites the link element or
  re-enables the channel for every descriptor. The follow-up can
  additionally avoid some stop/restart gaps by appending while running.

- dw_edma_core_ll_cur_idx() and dw_edma_core_ll_irq_clear() are not used
  until the follow-up. They remain here because this is a literal split of
  v5 patches 1-10.


Testing with this v6 (split-out prep series)
============================================

I tested this prep series on the following two testbeds:

- eDMA: RK3588 Rock 5B, DWC PCIe v5.60a
- HDMA: SpacemiT K3, DWC PCIe v6.30a [1]

1. fio

   The fio setup uses nvmet_pci_epf with a null_blk-backed namespace,
   runtime=30s, ramp_time=5s. The "Before" values reuse the baseline
   measurements reported with v2. The "After" values are three
   consecutive v6 runs.

   - eDMA (RK3588)

     Summary by group (BW delta %)
       all          n=26 mean=  +4.9 median=  +7.1 min= -33.3 max= +36.8
       read         n=14 mean=  +8.4 median= +10.2 min= -33.3 max= +31.7
       write        n=11 mean=  +0.7 median=  -0.3 min= -23.1 max= +36.8
       qd32         n=16 mean=  +5.3 median=  +9.9 min= -20.5 max= +31.7
       q1           n= 9 mean=  +4.5 median=  +4.7 min= -33.3 max= +36.8
       small 4K     n= 6 mean= +13.8 median= +11.9 min=  +9.6 max= +20.8
       large >=128K n=20 mean=  +2.2 median=  +0.5 min= -33.3 max= +36.8

   - HDMA (SpacemiT K3)

     Summary by group (BW delta %)
       all          n=26 mean= +21.5 median= +11.4 min= -23.4 max= +71.1
       read         n=14 mean= +15.3 median= +10.5 min= -23.4 max= +69.9
       write        n=11 mean= +31.0 median= +44.6 min=  -6.2 max= +71.1
       qd32         n=16 mean= +25.7 median= +13.6 min=  -8.3 max= +69.9
       q1           n= 9 mean= +16.1 median=  +7.0 min= -23.4 max= +71.1
       small 4K     n= 6 mean= +26.6 median= +16.8 min=  -6.2 max= +69.9
       large >=128K n=20 mean= +20.0 median= +11.4 min= -23.4 max= +71.1

2. pci_endpoint_test

   READ_TEST and WRITE_TEST passed with this v6 prep series on both
   testbeds.

[1] K3 was tested on an Ubuntu kernel with the prerequisite patches
    backported (+ some tweaks on top), not directly on the upstream
    base. The "Before" and "After" kernels differ only by this series.


Thanks for reviewing.

Best regards,
Koichiro
---
Changes in v6 (from v5 patch 1-10):
  - No changes.

Links to the original aggregate series:
  v5: https://lore.kernel.org/r/20260812155721.2807506-1-den@xxxxxxxxxxxxx/
  v4: https://lore.kernel.org/r/20260729143036.3087722-1-den@xxxxxxxxxxxxx/
  v3: https://lore.kernel.org/r/20260727170323.2321369-1-den@xxxxxxxxxxxxx/
  v2: https://lore.kernel.org/r/20260723084150.521366-1-den@xxxxxxxxxxxxx/
  v1: https://lore.kernel.org/r/20260615154111.2174161-1-den@xxxxxxxxxxxxx/


Frank Li (3):
  dmaengine: dw-edma: Add dw_edma_core_ll_cur_idx() to get current LL
    entry index
  dmaengine: dw-edma: Make DMA link list work as a circular buffer
  dmaengine: dw-edma: Move callback result helper before LL helpers

Koichiro Den (7):
  dmaengine: dw-edma: Add dw_edma_core_ll_clear() to clear LL
    control-word
  dmaengine: dw-edma: Factor out linked-list transfer start
  dmaengine: dw-edma: Dispatch DONE interrupts by channel request
  dmaengine: dw-edma: Centralize LL doorbell decisions
  dmaengine: dw-edma: Prepare LL progress event handling
  dmaengine: dw-edma: Prepare deferred IRQ reporting for LL events
  dmaengine: dw-edma: Prepare LL kicks for event serialization

 drivers/dma/dw-edma/dw-edma-core.c    | 341 ++++++++++++++++++--------
 drivers/dma/dw-edma/dw-edma-core.h    |  67 ++++-
 drivers/dma/dw-edma/dw-edma-v0-core.c |  59 +++--
 drivers/dma/dw-edma/dw-hdma-v0-core.c |  59 +++--
 include/linux/dma/edma.h              |   2 +-
 5 files changed, 377 insertions(+), 151 deletions(-)

base-commit: 0d995da5fb97e8c312834575604d4423eb6225b7
-- 
2.51.0