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

From: Allen

Date: Sun Oct 18 2026 - 17:17:20 EST

> >
> > 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

Apologies for the delayed response. yes. There's a handful of
dmaengine client-completion
tasklets outside drivers/dma/ as well. Since this series is already
queued, I'd rather not grow
it further at this point. I'll send conversions for those as a
follow-up series once this lands.

Thanks,
Allen

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

--
- Allen