Re: [PATCH] dmaengine: sun6i: constrain descriptor addresses through the DMA mask

[Frank Li]

On Wed, Oct 21, 2026 at 03:11:29PM -0600, James Hilliard wrote:
> Descriptor allocations pass GFP_DMA32 to dma_pool_alloc(). The DMA API
> chooses the memory zone from the device address mask, rather than accepting
> zone-selection flags from the driver. These flags can also reach the pool
> metadata allocation and trigger a slab allocator warning, as observed on
> H616 when preparing the first UART receive-DMA chain.
>
> Set a 32-bit coherent DMA mask before creating the descriptor pool and
> remove GFP_DMA32 from its allocations. The driver does not encode the
> extra descriptor-address bits supported by some variants, so descriptor
> links must remain below 4 GiB. Keep the streaming mask unchanged for
> variants with wider source and destination addresses.

Spouse other dma address in src/dest in descriptor also limited to 32bit.

Do you means only descripor address have 32bit limiation, other have not
such limiation?

Frank
>
> Fixes: ec31c5c59492 ("dmaengine: sun6i: Add support for 34-bit physical addresses")
> Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>
> ---
>  drivers/dma/sun6i-dma.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index 7704b016aed8..0ef6ed1f936e 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c
> @@ -684,7 +684,7 @@ static struct dma_async_tx_descriptor *sun6i_dma_prep_dma_memcpy(
>  	if (!txd)
>  		return NULL;
>
> -	v_lli = dma_pool_alloc(sdev->pool, GFP_DMA32 | GFP_NOWAIT, &p_lli);
> +	v_lli = dma_pool_alloc(sdev->pool, GFP_NOWAIT, &p_lli);
>  	if (!v_lli) {
>  		dev_err(sdev->slave.dev, "Failed to alloc lli memory\n");
>  		goto err_txd_free;
> @@ -743,7 +743,7 @@ static struct dma_async_tx_descriptor *sun6i_dma_prep_slave_sg(
>  		return NULL;
>
>  	for_each_sg(sgl, sg, sg_len, i) {
> -		v_lli = dma_pool_alloc(sdev->pool, GFP_DMA32 | GFP_NOWAIT, &p_lli);
> +		v_lli = dma_pool_alloc(sdev->pool, GFP_NOWAIT, &p_lli);
>  		if (!v_lli)
>  			goto err_lli_free;
>
> @@ -826,7 +826,7 @@ static struct dma_async_tx_descriptor *sun6i_dma_prep_dma_cyclic(
>  		return NULL;
>
>  	for (i = 0; i < periods; i++) {
> -		v_lli = dma_pool_alloc(sdev->pool, GFP_DMA32 | GFP_NOWAIT, &p_lli);
> +		v_lli = dma_pool_alloc(sdev->pool, GFP_NOWAIT, &p_lli);
>  		if (!v_lli) {
>  			dev_err(sdev->slave.dev, "Failed to alloc lli memory\n");
>  			goto err_lli_free;
> @@ -1345,6 +1345,11 @@ static int sun6i_dma_probe(struct platform_device *pdev)
>  		return PTR_ERR(sdc->rstc);
>  	}
>
> +	/* This driver uses unextended 32-bit addresses for descriptor links. */
> +	ret = dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32));
> +	if (ret)
> +		return ret;
> +
>  	sdc->pool = dmam_pool_create(dev_name(&pdev->dev), &pdev->dev,
>  				     sizeof(struct sun6i_dma_lli), 4, 0);
>  	if (!sdc->pool) {
>
> ---
> base-commit: 93f51579e7df248780214094418f205253383cc5
> change-id: 20261021-submit-sun6i-dma-descriptor-mask-v1-35bb381b932a
>
> Best regards,
> --
> James Hilliard <james.hilliard1@xxxxxxxxx>
>