linux-kernel - Re: Re: [PATCH] dmaengine: sun6i: Set the maximum segment size

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Date:   Tue, 21 Jun 2022 06:12:53 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Chen-Yu Tsai <wens@...e.org>, Vinod Koul <vkoul@...nel.org>,
        Samuel Holland <samuel@...lland.org>
Cc:     dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev
Subject: Re: Re: [PATCH] dmaengine: sun6i: Set the maximum segment size

Dne torek, 21. junij 2022 ob 02:20:11 CEST je Samuel Holland napisal(a):
> Hi Jernej,
> 
> On 6/20/22 1:28 PM, Jernej Škrabec wrote:
> > Dne petek, 17. junij 2022 ob 05:42:09 CEST je Samuel Holland napisal(a):
> >> The sun6i DMA engine supports segment sizes up to 2^25-1 bytes. This is
> >> explicitly stated in newer SoC documentation (H6, D1), and it is implied
> >> in older documentation by the 25-bit width of the "bytes left in the
> >> current segment" register field.
> > 
> > At least A10 user manual says 128k max in description for Byte Counter 
> > register (0x100+N*0x20+0xC), although field size is defined as 23:0, but 
that's 
> > still less than 2^25-1. A20 supports only 128k too according to manual. 
New 
> > quirk should be introduced for this.
> 
> Thanks for checking this. A10 and A20 use a separate driver (sun4i-dma). 
That
> driver will also benefit from setting the max segment size, so I will send a
> patch for it.
> 
> I think all of the variants supported by sun6i-dma have the same segment 
size
> capability, so no quirk is needed here.

Ah, yes. Then this patch is:
Reviewed-by: Jernej Skrabec <jernej.skrabec@...il.com>

Best regards,
Jernej

> 
> Regards,
> Samuel
> 
> >>
> >> Exposing the real segment size limit (instead of the 64k default)
> >> reduces the number of SG list segments needed for a transaction.
> >>
> >> Signed-off-by: Samuel Holland <samuel@...lland.org>
> >> ---
> >> Tested on A64, verified that the maximum ALSA PCM period increased, and
> >> that audio playback still worked.
> >>
> >>  drivers/dma/sun6i-dma.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> >> index b7557f437936..1425f87d97b7 100644
> >> --- a/drivers/dma/sun6i-dma.c
> >> +++ b/drivers/dma/sun6i-dma.c
> >> @@ -9,6 +9,7 @@
> >>  
> >>  #include <linux/clk.h>
> >>  #include <linux/delay.h>
> >> +#include <linux/dma-mapping.h>
> >>  #include <linux/dmaengine.h>
> >>  #include <linux/dmapool.h>
> >>  #include <linux/interrupt.h>
> >> @@ -1334,6 +1335,8 @@ static int sun6i_dma_probe(struct platform_device 
> > *pdev)
> >>  	INIT_LIST_HEAD(&sdc->pending);
> >>  	spin_lock_init(&sdc->lock);
> >>  
> >> +	dma_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(25));
> >> +
> >>  	dma_cap_set(DMA_PRIVATE, sdc->slave.cap_mask);
> >>  	dma_cap_set(DMA_MEMCPY, sdc->slave.cap_mask);
> >>  	dma_cap_set(DMA_SLAVE, sdc->slave.cap_mask);
> >> -- 
> >> 2.35.1
> >>
> >>
> > 
> > 
> 
>