netdev - Re: [RFC PATCH v3 22/35] dmaengine: dw-edma: Serialize RMW on shared interrupt registers

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Message-ID: <aUVjqbk1tQjJ1AEh@lizhi-Precision-Tower-5810>
Date: Fri, 19 Dec 2025 09:39:37 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: dave.jiang@...el.com, ntb@...ts.linux.dev, linux-pci@...r.kernel.org,
	dmaengine@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
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Subject: Re: [RFC PATCH v3 22/35] dmaengine: dw-edma: Serialize RMW on shared
 interrupt registers

On Thu, Dec 18, 2025 at 12:15:56AM +0900, Koichiro Den wrote:
> The per-direction int_mask and linked_list_err_en registers are shared
> between all channels. Updating them requires a read-modify-write
> sequence, which can lose concurrent updates when multiple channels are
> started in parallel. This may leave interrupts masked and stall
> transfers under high load.
>
> Protect the RMW sequences with dw->lock.
>
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---

I just posted a similar patch
https://lore.kernel.org/imx/20251212-edma_ll-v1-1-fc863d9f5ca3@nxp.com/

It change some method and I am working on add new request during dma engine
running.

At least, you can base on above thread.

Frank

>  drivers/dma/dw-edma/dw-edma-core.h    |  3 ++-
>  drivers/dma/dw-edma/dw-edma-v0-core.c | 13 ++++++++++---
>  2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
> index f652d2e38843..d393976a8bfc 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.h
> +++ b/drivers/dma/dw-edma/dw-edma-core.h
> @@ -118,7 +118,8 @@ struct dw_edma {
>
>  	struct dw_edma_chan		*chan;
>
> -	raw_spinlock_t			lock;		/* Only for legacy */
> +	/* For legacy + shared regs RMW among channels */
> +	raw_spinlock_t			lock;
>
>  	struct dw_edma_chip             *chip;
>
> diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
> index 42a254eb9379..770b011ba3e4 100644
> --- a/drivers/dma/dw-edma/dw-edma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
> @@ -369,7 +369,8 @@ static void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
>  {
>  	struct dw_edma_chan *chan = chunk->chan;
>  	struct dw_edma *dw = chan->dw;
> -	u32 tmp;
> +	unsigned long flags;
> +	u32 tmp, orig;
>
>  	dw_edma_v0_core_write_chunk(chunk);
>
> @@ -413,7 +414,9 @@ static void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
>  			}
>  		}
>  		/* Interrupt mask/unmask - done, abort */
> +		raw_spin_lock_irqsave(&dw->lock, flags);
>  		tmp = GET_RW_32(dw, chan->dir, int_mask);
> +		orig = tmp;
>  		if (chan->irq_mode == DW_EDMA_CH_IRQ_REMOTE) {
>  			tmp |= FIELD_PREP(EDMA_V0_DONE_INT_MASK, BIT(chan->id));
>  			tmp |= FIELD_PREP(EDMA_V0_ABORT_INT_MASK, BIT(chan->id));
> @@ -421,11 +424,15 @@ static void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
>  			tmp &= ~FIELD_PREP(EDMA_V0_DONE_INT_MASK, BIT(chan->id));
>  			tmp &= ~FIELD_PREP(EDMA_V0_ABORT_INT_MASK, BIT(chan->id));
>  		}
> -		SET_RW_32(dw, chan->dir, int_mask, tmp);
> +		if (tmp != orig)
> +			SET_RW_32(dw, chan->dir, int_mask, tmp);
>  		/* Linked list error */
>  		tmp = GET_RW_32(dw, chan->dir, linked_list_err_en);
> +		orig = tmp;
>  		tmp |= FIELD_PREP(EDMA_V0_LINKED_LIST_ERR_MASK, BIT(chan->id));
> -		SET_RW_32(dw, chan->dir, linked_list_err_en, tmp);
> +		if (tmp != orig)
> +			SET_RW_32(dw, chan->dir, linked_list_err_en, tmp);
> +		raw_spin_unlock_irqrestore(&dw->lock, flags);
>  		/* Channel control */
>  		SET_CH_32(dw, chan->dir, chan->id, ch_control1,
>  			  (DW_EDMA_V0_CCS | DW_EDMA_V0_LLE));
> --
> 2.51.0
>