[PATCH v4 00/33] dmaengine: migrate channel tasklets to WQ_BH

[Allen Pais <allen.lkml@gmail.com>]

Hi Vinod, Frank and Arnd,

This series moves DMAengine client completion bottom halves from private
tasklets to a common per-channel API backed by WQ_BH.

The first patch introduces the dmaengine_*_bh() API with a tasklet backend
and converts virt-dma to it. It also updates every driver that directly
accesses the removed virt_dma_chan tasklet, keeping the patch buildable on
its own. This separates the driver-facing API from its implementation
without changing callback context.

The second patch switches that backend to a dedicated WQ_BH | WQ_PERCPU
workqueue. WQ_BH keeps callbacks in softirq context, while the common API
centralizes initialization, scheduling, and synchronization. The
workqueue helpers remain internal to DMAengine, and dmaengine_kill_bh()
drains scheduled callbacks to preserve tasklet_kill() semantics.

The remaining patches convert driver-owned channel completion tasklets.
Tasklets used for controller-level processing, recovery, or other
non-client-callback work are deliberately left alone because the
appropriate replacement may differ by driver.

As agreed in the RFC discussion, selecting hardirq callback delivery is a
separate API change and is not part of this series.

Frank asked about DMAengine users outside drivers/dma/ that still
open-code completion tasklets. Those will be converted in a follow-up
series once this one has landed, to keep this set from growing further.

Earlier discussion:
https://lore.kernel.org/all/20260108080332.2341725-1-allen.lkml@gmail.com/

v2:
https://lore.kernel.org/all/cover.1785183549.git.allen.lkml@gmail.com/

v3:
https://lore.kernel.org/all/cover.1786384168.git.allen.lkml@gmail.com/

Changes since v3:
- post as a new thread instead of in reply to v3 (Andy)
- rebase onto v7.4-rc2. The ste_dma40 rework merged for 7.4-rc1 added
  tasklet_schedule() calls in the d40_queue_start() error paths and a
  devm action that kills the channel tasklets; both now use the BH
  helpers. fsldma and mv_xor gained tasklet_kill() calls in their channel
  remove and error paths, which are converted as well. zynqmp_dma and
  altera-msgdma only needed context fixes. The new amlogic-dma driver and
  the new at_hdmac channel cleanup path kill the virt-dma channel tasklet
  directly and are converted in 01/33.
- drop the DW DMA patch (v3 31/34). Andy considers it unneeded churn
  ahead of a larger cleanup of that driver.
- pl330: initialize the channel BH at probe time instead of in
  alloc_chan_resources(). dmaengine_init_bh() warns when called on an
  already initialized channel, and channels can be re-requested.
- txx9dmac: channels served by the shared controller interrupt keep
  scanning descriptors from the controller tasklet. v3 scheduled a BH
  that was never initialized for them.
- timb_dma: recompute TIMBDMA_IER from the channel BH once the channel
  has been finished, and drain the channel BHs on remove and in the probe
  error path.
- mpc512x: drain the channel BHs in mpc_dma_remove().
- sf-pdma: reset the retry budget when abandoning a descriptor, and
  spell out in the changelog how the new error path mirrors the done
  tasklet (Frank).
- hidma: leave hidma_free() unchanged (Frank). Drain the BH in
  free_chan_resources() and in remove(), after killing the low-level
  completion tasklet and before hidma_ll_uninit(), and add a
  device_synchronize() callback.
- qcom-gpi: synchronize the vchan before the channel ring is freed, and
  add a device_synchronize() callback.
- collect Frank Li's Reviewed-by from v3. I kept it on patches that only
  picked up mechanical conversions from the rebase (01, 06, 12, 17, 21,
  27, 30). timb_dma, txx9dmac, mpc512x, pl330 and qcom-gpi changed
  enough that I have not carried his tag forward on those.

The driver changes above came out of going through the Sashiko reports on
v3. Most of what it flagged are pre-existing teardown and locking issues
in the individual drivers that this series does not make worse; those are
out of scope here.

Review tags retained on unchanged standalone patches:
- 09/33 IOAT: Acked-by Dave Jiang
- 17/33 STE DMA40: Reviewed-by Linus Walleij (the rebase only added the
  mechanical conversions mentioned above)
- 27/33 PLX DMA and 33/33 Switchtec: Reviewed-by Logan Gunthorpe

Review tags received on v2 patches now folded into 01/33:
- v2 41/64 HSU: Reviewed-by Andy Shevchenko
- v2 60/64 BAM DMA: Acked-by Bartosz Golaszewski

The HSU and BAM DMA changes remain in 01/33, but those patch-specific
trailers are not attached to the substantially broader 37-file patch.
Andy and Bartosz are copied here and on 01/33 for visibility.

Testing:
- build-tested on top of v7.4-rc2 with W=1 for drivers/dma/, with no new
  warnings compared to the base commit:
  - arm64, x86_64 and arm allmodconfig
  - powerpc 44x/katmai_defconfig + AMCC_PPC440SPE_ADMA,
    mpc512x_defconfig + MPC512X_DMA, mpc85xx_smp_defconfig + FSL_DMA, and
    the same with FSL_DMA replaced by FSL_RAID
  - mips rbtx49xx_defconfig + TXX9_DMAC
- every patch builds on its own (drivers/dma/) with the arm64 and x86_64
  allmodconfig configurations
- the series also applies cleanly on dmaengine/next (currently v7.4-rc1)
- scripts/checkpatch.pl --strict is clean on all 33 patches
- the sf-pdma and hidma changes are compile-tested only; testing on
  hardware would be appreciated

Allen Pais (33):
  dmaengine: add tasklet-backed channel BH helpers
  dmaengine: back channel BH helpers with WQ_BH
  dmaengine: apple-admac: use dmaengine BH callback
  dmaengine: at_xdmac: move irq bottom half to dmaengine BH
  dmaengine: ep93xx: hook callbacks via dmaengine BH
  dmaengine: fsldma: migrate tasklet to dmaengine BH
  dmaengine: fsl_raid: run completions via dmaengine BH
  dmaengine: imx-dma: flip per-chan tasklet to dmaengine BH
  dmaengine: ioat: convert cleanup tasklet to dmaengine BH
  dmaengine: mmp_pdma: replace per-chan tasklet with dmaengine BH
  dmaengine: mmp_tdma: hook completions to dmaengine BH
  dmaengine: mv_xor: convert irq tasklet to dmaengine BH
  dmaengine: mxs-dma: use dmaengine BH scheduling
  dmaengine: nbpfaxi: switch callbacks to dmaengine BH
  dmaengine: pch_dma: convert tasklet to dmaengine BH
  dmaengine: ppc4xx: replace irq tasklet with dmaengine BH
  dmaengine: ste_dma40: convert per-channel tasklet to dmaengine BH
  dmaengine: xgene-dma: wire descriptor cleanup to dmaengine BH
  dmaengine: xilinx-dma: use dmaengine BH instead of tasklets
  dmaengine: xilinx-dpdma: kill vchan BH on remove
  dmaengine: zynqmp-dma: switch completion tasklet to dmaengine BH
  dmaengine: tegra20-apb: use channel BH helpers
  dmaengine: timb_dma: route callbacks via channel BH
  dmaengine: txx9dmac: route callbacks via channel BH
  dmaengine: mv_xor_v2: use channel BH helpers
  dmaengine: mpc512x: route callbacks via channel BH
  dmaengine: plx_dma: use channel BH helpers
  dmaengine: sf-pdma: route error callbacks through channel BH
  dmaengine: pl330: route callbacks via channel BH
  dmaengine: altera-msgdma: use channel BH helpers
  dmaengine: hidma: defer callbacks via channel BH
  dmaengine: qcom-gpi: defer callbacks via vchan
  dmaengine: switchtec: use channel BH helpers

 drivers/dma/altera-msgdma.c                   | 14 +--
 drivers/dma/amlogic-dma.c                     |  4 +-
 drivers/dma/apple-admac.c                     | 16 ++--
 drivers/dma/at_hdmac.c                        |  2 +-
 drivers/dma/at_xdmac.c                        | 13 ++-
 drivers/dma/bcm2835-dma.c                     |  2 +-
 drivers/dma/dma-axi-dmac.c                    | 10 ++-
 drivers/dma/dma-jz4780.c                      |  2 +-
 drivers/dma/dmaengine.c                       | 89 ++++++++++++++++++-
 .../dma/dw-axi-dmac/dw-axi-dmac-platform.c    |  2 +-
 drivers/dma/dw-edma/dw-edma-core.c            |  2 +-
 drivers/dma/ep93xx_dma.c                      | 12 ++-
 drivers/dma/fsl-edma-common.c                 |  2 +-
 drivers/dma/fsl-qdma.c                        |  2 +-
 drivers/dma/fsl_raid.c                        | 11 +--
 drivers/dma/fsl_raid.h                        |  1 -
 drivers/dma/fsldma.c                          | 12 +--
 drivers/dma/fsldma.h                          |  1 -
 drivers/dma/hisi_dma.c                        |  2 +-
 drivers/dma/hsu/hsu.c                         |  2 +-
 drivers/dma/idma64.c                          |  4 +-
 drivers/dma/img-mdc-dma.c                     |  2 +-
 drivers/dma/imx-dma.c                         | 26 +++---
 drivers/dma/imx-sdma.c                        |  4 +-
 drivers/dma/ioat/dma.c                        | 14 +--
 drivers/dma/ioat/dma.h                        |  3 +-
 drivers/dma/ioat/init.c                       |  2 +-
 drivers/dma/k3dma.c                           |  2 +-
 drivers/dma/loongson/loongson1-apb-dma.c      |  2 +-
 drivers/dma/mediatek/mtk-cqdma.c              |  2 +-
 drivers/dma/mediatek/mtk-hsdma.c              |  2 +-
 drivers/dma/mediatek/mtk-uart-apdma.c         |  4 +-
 drivers/dma/mmp_pdma.c                        | 13 ++-
 drivers/dma/mmp_tdma.c                        |  9 +-
 drivers/dma/mpc512x_dma.c                     | 78 ++++++++++------
 drivers/dma/mv_xor.c                          | 14 +--
 drivers/dma/mv_xor.h                          |  2 -
 drivers/dma/mv_xor_v2.c                       | 20 ++---
 drivers/dma/mxs-dma.c                         | 11 ++-
 drivers/dma/nbpfaxi.c                         | 13 ++-
 drivers/dma/owl-dma.c                         |  2 +-
 drivers/dma/pch_dma.c                         | 14 +--
 drivers/dma/pl330.c                           | 19 ++--
 drivers/dma/plx_dma.c                         | 12 +--
 drivers/dma/ppc4xx/adma.c                     | 14 +--
 drivers/dma/ppc4xx/adma.h                     |  2 -
 drivers/dma/pxa_dma.c                         |  2 +-
 drivers/dma/qcom/bam_dma.c                    |  4 +-
 drivers/dma/qcom/gpi.c                        | 27 +++++-
 drivers/dma/qcom/hidma.c                      | 24 ++++-
 drivers/dma/qcom/qcom_adm.c                   |  4 +-
 drivers/dma/sa11x0-dma.c                      |  2 +-
 drivers/dma/sf-pdma/sf-pdma.c                 | 18 +++-
 drivers/dma/sprd-dma.c                        |  2 +-
 drivers/dma/st_fdma.c                         |  2 +-
 drivers/dma/ste_dma40.c                       | 29 +++---
 drivers/dma/sun6i-dma.c                       |  2 +-
 drivers/dma/switchtec_dma.c                   | 16 ++--
 drivers/dma/tegra186-gpc-dma.c                |  2 +-
 drivers/dma/tegra20-apb-dma.c                 | 18 ++--
 drivers/dma/tegra210-adma.c                   |  2 +-
 drivers/dma/ti/edma.c                         |  2 +-
 drivers/dma/ti/k3-udma.c                      | 12 +--
 drivers/dma/ti/omap-dma.c                     |  2 +-
 drivers/dma/timb_dma.c                        | 41 +++++++--
 drivers/dma/txx9dmac.c                        | 10 +--
 drivers/dma/txx9dmac.h                        |  1 -
 drivers/dma/virt-dma.c                        | 12 +--
 drivers/dma/virt-dma.h                        |  7 +-
 drivers/dma/xgene-dma.c                       | 19 ++--
 drivers/dma/xilinx/xilinx_dma.c               | 20 ++---
 drivers/dma/xilinx/xilinx_dpdma.c             |  1 +
 drivers/dma/xilinx/zynqmp_dma.c               | 19 ++--
 include/linux/dmaengine.h                     | 28 ++++++
 74 files changed, 503 insertions(+), 316 deletions(-)


base-commit: 7475ea8b58616b33c04afb976cf0fbaad9dd63fb
-- 
2.43.0