[PATCH v4 0/7] dmaengine: dw: serialize completion and termination

[James Hilliard]

Keep client callbacks in the controller tasklet while preserving polled
completion. Serialize descriptor ownership across completion, error
recovery and termination, and wait for callbacks before a client reuses
its resources.

The first two patches serialize channel-completion and error-recovery
handling with termination. The next two complete cookies under the channel
lock and separate residue calculation from completion processing. Channel
release and device_synchronize then gain tasklet draining before the final
patch adds the deferred completion list and tasklet-only notification.

The series adapts Serge Semin's channel-restart and callback fixes [0-2].
Polling continues to advance cookies and software-LLP blocks, while client
notifications run from the controller tasklet. Synchronization preserves
pending tasklet runs from other channels.

[0] https://lore.kernel.org/r/20240911184710.4207-1-fancer.lancer@xxxxxxxxx
[1] https://lore.kernel.org/r/20240911184710.4207-2-fancer.lancer@xxxxxxxxx
[2] https://lore.kernel.org/r/20240911184710.4207-3-fancer.lancer@xxxxxxxxx

Assisted-by: Codex:gpt-6-astra
Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>

---
Changes in v4:
- Split v3's callback-deferral patch into cookie accounting, residue
  calculation, channel-release draining and callback-deferral patches,
  following Frank's review. The resulting seven-patch series preserves
  v3's final implementation.
- Place device_synchronize before callback deferral so clients can drain
  deferred notifications when the completion list is introduced.
- Carry Frank's Reviewed-by tags on the unchanged channel-completion,
  error-recovery and device_synchronize patches.
- Link to v3: https://patch.msgid.link/20261023-submit-dw-dma-synchronize-v1-v3-0-c62bf048f5ce@xxxxxxxxx

Changes in v3:
- Order channel-completion and error-recovery locking before callback
  deferral, retaining four patches.
- Require a locked RAW.XFER event before retiring a transfer; zero source
  residue alone cannot establish destination completion.
- Preserve polled completion and software-LLP progress in tx_status(),
  queuing client notifications for the controller tasklet.
- Serialize cookie updates with termination and report queued residue.
- Drain deferred notifications on channel release and let a pending
  tasklet return without MMIO after the last channel is released.
- Adapt Serge's two patches and retain his authorship and revision notes.
  Drop the Tested-by tags that covered their earlier implementations.
- Identify the introduction of the synchronization API in the final
  patch's Fixes tag.
- Link to v2: https://patch.msgid.link/20261022-submit-dw-dma-synchronize-v1-v2-0-5244e94dca8c@xxxxxxxxx

Changes in v2:
- Carry Serge Semin's two posted fixes before the synchronization change,
  preserving his authorship and revision notes. Add the requested stable
  Cc trailers and Andy Shevchenko's Tested-by tags to those unchanged fixes.
- Add a separate error-recovery fix for stale error status, empty channel
  lists and software-LLP state when terminating or restarting a channel.
- Use tasklet_disable()/tasklet_enable() instead of tasklet_kill() so
  synchronization preserves scheduling requests from other channels.
- Explain descriptor ownership during termination and acknowledge the
  shared-tasklet scheduling race reported by Sashiko.
- Link to v1: https://patch.msgid.link/20261021-submit-dw-dma-synchronize-v1-v1-1-6af85c2d6f69@xxxxxxxxx

Revision history from Serge's series:

Link: https://lore.kernel.org/dmaengine/20240802080756.7415-1-fancer.lancer@xxxxxxxxx/
Changelog RFC:
- Add a new patch:
  [PATCH 2/2] dmaengine: dw: Fix XFER bit set, but channel not idle error
  fixing the "XFER bit set, but channel not idle" error.
- Instead of just dropping the dwc_scan_descriptors() method invocation
  calculate the residue in the Tx-status getter.

---
James Hilliard (4):
      dmaengine: dw: serialize error recovery with channel termination
      dmaengine: dw: complete cookies before releasing the channel lock
      dmaengine: dw: drain the tasklet before releasing channel resources
      dmaengine: dw: synchronize completion callbacks

Serge Semin (3):
      dmaengine: dw: Fix XFER bit set, but channel not idle error
      dmaengine: dw: calculate residue separately from completion
      dmaengine: dw: Prevent tx-status calling DMA-desc callback

 drivers/dma/dw/core.c | 307 ++++++++++++++++++++++++++------------------------
 drivers/dma/dw/regs.h |   1 +
 2 files changed, 160 insertions(+), 148 deletions(-)
---
base-commit: 93f51579e7df248780214094418f205253383cc5
change-id: 20261021-submit-dw-dma-synchronize-v1-e550f47fd1da

Best regards,
--  
James Hilliard <james.hilliard1@xxxxxxxxx>