Re: [PATCH 1/2] dmaengine: dw-axi-dmac: Fix AXI burst length encoding

[Frank Li <Frank.li@oss.nxp.com>]

On Fri, Aug 28, 2026 at 08:48:26AM +0800, Jia Wang wrote:
> The snps,axi-max-burst-len property describes the number of beats in an
> AXI burst, while the ARLEN and AWLEN fields encode that value minus one.
>
> The driver keeps axi_rw_burst_len as the actual burst length so that
> dma_device.max_burst reports the correct value. However, it also programs
> that unencoded value directly into the hardware fields. A value of 256
> therefore overflows the 8-bit fields and can cause AXI decode errors.
>
> Subtract one only when constructing hardware descriptors, while keeping
> the actual value for dma_device.max_burst.
>
> Fixes: c454d16a7d5a ("dmaengine: dw-axi-dmac: Burst length settings")
> Signed-off-by: Jia Wang <wangjia@ultrarisc.com>
> ---

suggest switch to use FIELD_PREP() later

Reviewed-by: Frank Li <Frank.Li@nxp.com>

>  drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> index eebed2474210..742e08cfab43 100644
> --- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> +++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> @@ -706,7 +706,7 @@ static int dw_axi_dma_set_hw_desc(struct axi_dma_chan *chan,
>  	ctlhi = CH_CTL_H_LLI_VALID;
>
>  	if (chan->chip->dw->hdata->restrict_axi_burst_len) {
> -		burst_len = chan->chip->dw->hdata->axi_rw_burst_len;
> +		burst_len = chan->chip->dw->hdata->axi_rw_burst_len - 1;
>  		ctlhi |= CH_CTL_H_ARLEN_EN | CH_CTL_H_AWLEN_EN |
>  			 burst_len << CH_CTL_H_ARLEN_POS |
>  			 burst_len << CH_CTL_H_AWLEN_POS;
> @@ -975,7 +975,7 @@ dma_chan_prep_dma_memcpy(struct dma_chan *dchan, dma_addr_t dst_adr,
>
>  		reg = CH_CTL_H_LLI_VALID;
>  		if (chan->chip->dw->hdata->restrict_axi_burst_len) {
> -			u32 burst_len = chan->chip->dw->hdata->axi_rw_burst_len;
> +			u32 burst_len = chan->chip->dw->hdata->axi_rw_burst_len - 1;
>
>  			reg |= (CH_CTL_H_ARLEN_EN |
>  				burst_len << CH_CTL_H_ARLEN_POS |
>
> --
> 2.34.1
>