linux-kernel - Re: [PATCH 4/4] dmaengine: axi-dmac: Use only EOT interrupts when doing scatter-gather

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Date:   Mon, 11 Dec 2023 17:31:24 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Nuno Sá <noname.nuno@...il.com>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] dmaengine: axi-dmac: Use only EOT interrupts when
 doing scatter-gather

On 04-12-23, 15:03, Paul Cercueil wrote:
> Instead of notifying userspace in the end-of-transfer (EOT) interrupt
> and program the hardware in the start-of-transfer (SOT) interrupt, we
> can do both things in the EOT, allowing us to mask the SOT, and halve
> the number of interrupts sent by the HDL core.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/dma/dma-axi-dmac.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
> index 5109530b66de..beed91a8238c 100644
> --- a/drivers/dma/dma-axi-dmac.c
> +++ b/drivers/dma/dma-axi-dmac.c
> @@ -415,6 +415,7 @@ static bool axi_dmac_transfer_done(struct axi_dmac_chan *chan,
>  			list_del(&active->vdesc.node);
>  			vchan_cookie_complete(&active->vdesc);
>  			active = axi_dmac_active_desc(chan);
> +			start_next = !!active;

Should this be in current patch, sounds like this should be a different
patch?

>  		}
>  	} else {
>  		do {
> @@ -1000,6 +1001,7 @@ static int axi_dmac_probe(struct platform_device *pdev)
>  	struct axi_dmac *dmac;
>  	struct regmap *regmap;
>  	unsigned int version;
> +	u32 irq_mask = 0;
>  	int ret;
>  
>  	dmac = devm_kzalloc(&pdev->dev, sizeof(*dmac), GFP_KERNEL);
> @@ -1067,7 +1069,10 @@ static int axi_dmac_probe(struct platform_device *pdev)
>  
>  	dma_dev->copy_align = (dmac->chan.address_align_mask + 1);
>  
> -	axi_dmac_write(dmac, AXI_DMAC_REG_IRQ_MASK, 0x00);
> +	if (dmac->chan.hw_sg)
> +		irq_mask |= AXI_DMAC_IRQ_SOT;
> +
> +	axi_dmac_write(dmac, AXI_DMAC_REG_IRQ_MASK, irq_mask);
>  
>  	if (of_dma_is_coherent(pdev->dev.of_node)) {
>  		ret = axi_dmac_read(dmac, AXI_DMAC_REG_COHERENCY_DESC);
> -- 
> 2.42.0
> 

-- 
~Vinod