Re: [PATCH v6 1/8] dmaengine: dw-edma: Deassert emulated interrupts in the IRQ handler

[Frank Li <Frank.li@nxp.com>]

On Mon, Feb 09, 2026 at 09:53:09PM +0900, Koichiro Den wrote:
> Some DesignWare eDMA instances support "interrupt emulation", where a
> software write can assert the IRQ line without setting the normal
> DONE/ABORT status bits.
>
> With a shared IRQ handler the driver cannot reliably distinguish an
> emulated interrupt from a real one by only looking at DONE/ABORT status
> bits. Leaving the emulated IRQ asserted may leave a level-triggered IRQ
> line permanently asserted.
>
> Add a core callback, .ack_emulated_irq(), to perform the core-specific
> deassert sequence and call it from the read/write/common IRQ handlers.
> Note that previously a direct software write could assert the emulated
> IRQ without DMA activity, leading to the interrupt never getting
> deasserted. This patch resolves it.
>
> For v0, a zero write to INT_CLEAR deasserts the emulated IRQ and is a
> no-op for real interrupts. HDMA is not tested or verified and is
> therefore unsupported for now.
>
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>  drivers/dma/dw-edma/dw-edma-core.c    | 48 ++++++++++++++++++++++++---
>  drivers/dma/dw-edma/dw-edma-core.h    | 10 ++++++
>  drivers/dma/dw-edma/dw-edma-v0-core.c | 11 ++++++
>  3 files changed, 64 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 8e5f7defa6b6..fe131abf1ca3 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -663,7 +663,24 @@ static void dw_edma_abort_interrupt(struct dw_edma_chan *chan)
>  	chan->status = EDMA_ST_IDLE;
>  }
>
> -static inline irqreturn_t dw_edma_interrupt_write(int irq, void *data)
> +static inline irqreturn_t dw_edma_interrupt_emulated(void *data)
> +{
> +	struct dw_edma_irq *dw_irq = data;
> +	struct dw_edma *dw = dw_irq->dw;
> +
> +	/*
> +	 * Interrupt emulation may assert the IRQ line without updating the
> +	 * normal DONE/ABORT status bits. With a shared IRQ handler we
> +	 * cannot reliably detect such events by status registers alone, so
> +	 * always perform the core-specific deassert sequence.
> +	 */
> +	if (dw_edma_core_ack_emulated_irq(dw))
> +		return IRQ_NONE;
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static inline irqreturn_t dw_edma_interrupt_write_inner(int irq, void *data)
>  {
>  	struct dw_edma_irq *dw_irq = data;
>
> @@ -672,7 +689,7 @@ static inline irqreturn_t dw_edma_interrupt_write(int irq, void *data)
>  				       dw_edma_abort_interrupt);
>  }
>
> -static inline irqreturn_t dw_edma_interrupt_read(int irq, void *data)
> +static inline irqreturn_t dw_edma_interrupt_read_inner(int irq, void *data)
>  {
>  	struct dw_edma_irq *dw_irq = data;
>
> @@ -681,12 +698,33 @@ static inline irqreturn_t dw_edma_interrupt_read(int irq, void *data)
>  				       dw_edma_abort_interrupt);
>  }
>
> -static irqreturn_t dw_edma_interrupt_common(int irq, void *data)
> +static inline irqreturn_t dw_edma_interrupt_write(int irq, void *data)
> +{
> +	irqreturn_t ret = IRQ_NONE;
> +
> +	ret |= dw_edma_interrupt_write_inner(irq, data);
> +	ret |= dw_edma_interrupt_emulated(data);
> +
> +	return ret;
> +}
> +
> +static inline irqreturn_t dw_edma_interrupt_read(int irq, void *data)
> +{
> +	irqreturn_t ret = IRQ_NONE;
> +
> +	ret |= dw_edma_interrupt_read_inner(irq, data);
> +	ret |= dw_edma_interrupt_emulated(data);
> +
> +	return ret;
> +}
> +
> +static inline irqreturn_t dw_edma_interrupt_common(int irq, void *data)
>  {
>  	irqreturn_t ret = IRQ_NONE;
>
> -	ret |= dw_edma_interrupt_write(irq, data);
> -	ret |= dw_edma_interrupt_read(irq, data);
> +	ret |= dw_edma_interrupt_write_inner(irq, data);
> +	ret |= dw_edma_interrupt_read_inner(irq, data);
> +	ret |= dw_edma_interrupt_emulated(data);
>
>  	return ret;
>  }
> diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
> index 71894b9e0b15..50b87b63b581 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.h
> +++ b/drivers/dma/dw-edma/dw-edma-core.h
> @@ -126,6 +126,7 @@ struct dw_edma_core_ops {
>  	void (*start)(struct dw_edma_chunk *chunk, bool first);
>  	void (*ch_config)(struct dw_edma_chan *chan);
>  	void (*debugfs_on)(struct dw_edma *dw);
> +	void (*ack_emulated_irq)(struct dw_edma *dw);
>  };
>
>  struct dw_edma_sg {
> @@ -206,4 +207,13 @@ void dw_edma_core_debugfs_on(struct dw_edma *dw)
>  	dw->core->debugfs_on(dw);
>  }
>
> +static inline int dw_edma_core_ack_emulated_irq(struct dw_edma *dw)
> +{
> +	if (!dw->core->ack_emulated_irq)
> +		return -EOPNOTSUPP;
> +
> +	dw->core->ack_emulated_irq(dw);
> +	return 0;
> +}
> +
>  #endif /* _DW_EDMA_CORE_H */
> diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
> index b75fdaffad9a..82b9c063c10f 100644
> --- a/drivers/dma/dw-edma/dw-edma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
> @@ -509,6 +509,16 @@ static void dw_edma_v0_core_debugfs_on(struct dw_edma *dw)
>  	dw_edma_v0_debugfs_on(dw);
>  }
>
> +static void dw_edma_v0_core_ack_emulated_irq(struct dw_edma *dw)
> +{
> +	/*
> +	 * Interrupt emulation may assert the IRQ without setting
> +	 * DONE/ABORT status bits. A zero write to INT_CLEAR deasserts the
> +	 * emulated IRQ, while being a no-op for real interrupts.
> +	 */
> +	SET_BOTH_32(dw, int_clear, 0);
> +}
> +
>  static const struct dw_edma_core_ops dw_edma_v0_core = {
>  	.off = dw_edma_v0_core_off,
>  	.ch_count = dw_edma_v0_core_ch_count,
> @@ -517,6 +527,7 @@ static const struct dw_edma_core_ops dw_edma_v0_core = {
>  	.start = dw_edma_v0_core_start,
>  	.ch_config = dw_edma_v0_core_ch_config,
>  	.debugfs_on = dw_edma_v0_core_debugfs_on,
> +	.ack_emulated_irq = dw_edma_v0_core_ack_emulated_irq,
>  };
>
>  void dw_edma_v0_core_register(struct dw_edma *dw)
> --
> 2.51.0
>