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

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Message-ID: <381267f0a20d162f87b83c0af6949a9f997ea83e.camel@crapouillou.net>
Date:   Mon, 11 Dec 2023 13:20:38 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Vinod Koul <vkoul@...nel.org>
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

Hi Vinod,

Le lundi 11 décembre 2023 à 17:31 +0530, Vinod Koul a écrit :
> 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?

It belongs here. This line is what allows a new transfer to be
programmed from the EOT. Since we disable the SOT interrupt, if we
remove that line, the driver won't work.

Cheers,
-Paul

> 
> >  		}
> >  	} 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
> > 
>