Re: [PATCH v4 11/24] dmaengine: dw-edma: Serialize LL event capture with channel kicks

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Ringing the doorbell can race with a hardware interrupt, clearing and permanently losing a pending DMA completion event.
--

--- Patch [11]: [PATCH v4 11/24] dmaengine: dw-edma: Serialize LL event capture with channel kicks ---
commit 56231794b3b46dd52a7c7f61f0def40f1fed9890
Author: Koichiro Den <den@valinux.co.jp>

dmaengine: dw-edma: Serialize LL event capture with channel kicks
    
This commit introduces an event lock to serialize interrupt status reads,
clears, snapshot recording, and LL doorbell writes. It aims to prevent a
deferred handler from applying an event from a previous hardware run when a
doorbell starts a new run in between.

> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c

[ ... ]

> @@ -269,6 +317,17 @@ static void dw_edma_core_ll_sync(struct dw_edma_chan *chan)
>  static void dw_edma_core_ch_doorbell(struct dw_edma_chan *chan)
>  {
>  	dw_edma_core_ll_sync(chan);
> +
> +	guard(spinlock_irqsave)(dw_edma_event_lock(chan));
> +
> +	/*
> +	 * A recorded event belongs to the current ring and must be consumed
> +	 * before starting another hardware run.
> +	 */
> +	if (chan->ll_irq.event != DW_EDMA_LL_EVENT_NONE)
> +		return;
> +
> +	dw_edma_ll_event_discard_locked(chan);

[Severity: High]
Can this race with a hardware interrupt and permanently lose a completion event?

If dw_edma_core_ch_doorbell() is called (for example, when appending
descriptors to a running channel) exactly when the hardware finishes a burst
and asserts an interrupt, but before the hardirq handler can run,
chan->ll_irq.event will still be DW_EDMA_LL_EVENT_NONE.

The code will bypass the early return and unconditionally call
dw_edma_ll_event_discard_locked(), which clears the hardware interrupt
status.

Does this result in the interrupt being completely lost? If so, the software
state will permanently trail the hardware, which would cause the DMA channel
to stall indefinitely.

>  	dw_edma_core_do_ch_doorbell(chan);
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260729143036.3087722-1-den@valinux.co.jp?part=11