Re: [PATCH v3 00/34] dmaengine: migrate channel tasklets to WQ_BH

[Frank Li]

On Mon, Aug 10, 2026 at 11:09:01AM -0700, Allen Pais wrote:
> Hi Arnd, Vinod and Frank,
>
> 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.
>
> Earlier discussion:
> https://lore.kernel.org/all/20260108080332.2341725-1-allen.lkml@xxxxxxxxx/
>
> v2:
> https://lore.kernel.org/all/cover.1785183549.git.allen.lkml@xxxxxxxxx/
>
> Changes since v2:
> - rename the new public helpers and callback type from dma_chan_* to
>   dmaengine_* as requested by Vinod
> - update all direct virt_dma_chan tasklet users in patch 1, fixing the
>   intermediate build failures reported by Sashiko
> - fold the resulting 30 empty teardown patches, reducing the series from
>   64 to 34 patches without dropping any driver changes
> - rebase from Linux 7.2-rc5 to d58772d8520c (latest Linus master)
>
> Review tags retained on unchanged standalone patches:
> - 09/34 IOAT: Acked-by Dave Jiang
> - 17/34 STE DMA40: Reviewed-by Linus Walleij
> - 27/34 PLX DMA and 34/34 Switchtec: Reviewed-by Logan Gunthorpe
>
> Review tags received on v2 patches now folded into 01/34:
> - 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 01/34, but those patch-specific
> trailers are not attached to the substantially broader 35-file patch.
> Andy and Bartosz are copied here and on 01/34 for visibility.
>
> Testing:
> - x86_64 olddefconfig, make -j$(nproc) W=1 drivers/dma/
> - the same DMA build with patch 1 applied independently
> - scripts/checkpatch.pl --strict on all 34 patches
>
> Allen Pais (34):
>   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: dw: defer callbacks via channel BH
>   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/apple-admac.c                     | 16 ++--
>  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/dw/core.c                         | 42 +++++++--
>  drivers/dma/dw/regs.h                         |  1 +
>  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                          | 10 +--
>  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                     | 74 +++++++++------
>  drivers/dma/mv_xor.c                          | 12 +--
>  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                           | 18 ++--
>  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                        | 17 +++-
>  drivers/dma/qcom/hidma.c                      | 18 +++-
>  drivers/dma/qcom/qcom_adm.c                   |  4 +-
>  drivers/dma/sa11x0-dma.c                      |  2 +-
>  drivers/dma/sf-pdma/sf-pdma.c                 | 14 ++-
>  drivers/dma/sprd-dma.c                        |  2 +-
>  drivers/dma/st_fdma.c                         |  2 +-
>  drivers/dma/ste_dma40.c                       | 13 ++-
>  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                        | 21 +++--
>  drivers/dma/txx9dmac.c                        | 12 +--
>  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 ++--

There are some dmaengine code out of drivers/dma tree. Do you plan to
convert it also

Frank

>  include/linux/dmaengine.h                     | 28 ++++++
>  74 files changed, 482 insertions(+), 311 deletions(-)
>
> --
> 2.43.0