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

[Robin Murphy]

On 2022-06-17 04:42, Samuel Holland wrote:
> 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.
>
> 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@xxxxxxxxxxxx>
> ---
> 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));

Similarly to my comment on the DRM patch, "SZ_32M - 1" might be clearer 
here.

Thanks,
Robin.

> +
>   	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);