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Message-ID: <aYoFsMclytqtkc9N@lizhi-Precision-Tower-5810>
Date: Mon, 9 Feb 2026 11:05:04 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: vkoul@...nel.org, mani@...nel.org, cassel@...nel.org,
jingoohan1@...il.com, lpieralisi@...nel.org, kwilczynski@...nel.org,
robh@...nel.org, bhelgaas@...gle.com, kishon@...nel.org,
jdmason@...zu.us, allenbh@...il.com, dmaengine@...r.kernel.org,
linux-pci@...r.kernel.org, ntb@...ts.linux.dev,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/8] dmaengine: dw-edma: Deassert emulated interrupts
in the IRQ handler
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@...inux.co.jp>
> ---
Reviewed-by: Frank Li <Frank.Li@....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
>
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