Re: [PATCH v6 4/6] dmaengine: dw-edma: Add delegated channel request helpers

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Releasing a single delegated channel with `quiesce=true` on eDMA v0 hardware causes a data race on `engine_en` and incorrectly shuts down the entire DMA direction, disrupting all other local channels.
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--- Patch [4]: [PATCH v6 4/6] dmaengine: dw-edma: Add delegated channel request helpers ---
commit 0987248b986738e4870e25b1f36d8c9f2eb69d8b
Author: Koichiro Den <den@valinux.co.jp>

dmaengine: dw-edma: Add delegated channel request helpers

This commit adds DesignWare eDMA-specific helpers to request and release
hardware channels for delegation to a remote host. The release helper
supports quiescing the channel before restoring default routing and
releasing the DMAengine reservation.

> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 1f893dc54c793..4c0d2bba755b5 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
[ ... ]
> +void dw_edma_release_delegated_chan(struct dma_chan *dchan, bool quiesce)
> +{
> +	struct dw_edma_chan *chan;
> +
> +	if (!dchan)
> +		return;
> +
> +	chan = dchan2dw_edma_chan(dchan);
> +	if (quiesce && dw_edma_core_ch_quiesce(chan))

[Severity: High]
Does releasing a delegated channel with quiesce set to true unintentionally
disrupt all other active local channels in the same direction?

If an endpoint driver uses some channels locally while delegating others to a
remote host, this call to dw_edma_core_ch_quiesce() appears to escalate to a
direction-wide shutdown on eDMA v0 hardware:

drivers/dma/dw-edma/dw-edma-v0-core.c:dw_edma_v0_core_ch_quiesce() {
    ...
    return dw_edma_v0_core_dir_off(chan->dw, chan->dir);
}

dw_edma_v0_core_dir_off() forcefully masks interrupts for all channels in the
direction and locklessly clears the engine_en register via
dw_edma_v0_core_engine_disable():

drivers/dma/dw-edma/dw-edma-v0-core.c:dw_edma_v0_core_engine_disable() {
    ...
    SET_RW_32(dw, dir, engine_en, 0);
}

Since the per-channel delegation API does not enforce exclusive ownership of
the direction, does this cause a data race and abort ongoing DMA transfers on
unrelated active local channels?

> +		dev_warn(chan->dw->chip->dev,
> +			 "failed to quiesce delegated %s channel %u\n",
> +			 chan->dir == EDMA_DIR_WRITE ? "write" : "read",
> +			 chan->id);
> +
> +	scoped_guard(spinlock_irqsave, &chan->vc.lock)
> +		chan->irq_mode = dw_edma_get_default_irq_mode(chan);
> +
> +	dma_release_channel(dchan);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260804033855.2115817-1-den@valinux.co.jp?part=4