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Message-ID: <3494277.R56niFO833@kista>
Date: Mon, 20 Jun 2022 20:28:46 +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: Samuel Holland <samuel@...lland.org>, dmaengine@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH] dmaengine: sun6i: Set the maximum segment size
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.
Best regards,
Jernej
>
> 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
>
>
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