Hi Matthias!
One small comment, I'll test everything later on.

On Fri, 2019-10-11 at 20:48 +0200, matthias.bgg@kernel.org wrote:
> From: Matthias Brugger <mbrugger@suse.com>
> 
> Depending on the HW, the maximal usable DMA burst size can vary.
> If not set accordingly a timeout in the transmit queue happens and no
> package can be sent. Read to optional max-burst-sz property, if not
> present, fallback to the standard value.
> 
> Signed-off-by: Matthias Brugger <mbrugger@suse.com>
> ---
> 
>  drivers/net/ethernet/broadcom/genet/bcmgenet.c | 13 +++++++++++--
>  drivers/net/ethernet/broadcom/genet/bcmgenet.h |  1 +
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index 12cb77ef1081..a7bb822a6d83 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -2576,7 +2576,8 @@ static int bcmgenet_init_dma(struct bcmgenet_priv *priv)
>  	}
>  
>  	/* Init rDma */
> -	bcmgenet_rdma_writel(priv, DMA_MAX_BURST_LENGTH, DMA_SCB_BURST_SIZE);
> +	bcmgenet_rdma_writel(priv, priv->dma_max_burst_length,
> +			     DMA_SCB_BURST_SIZE);
>  
>  	/* Initialize Rx queues */
>  	ret = bcmgenet_init_rx_queues(priv->dev);
> @@ -2589,7 +2590,8 @@ static int bcmgenet_init_dma(struct bcmgenet_priv *priv)
>  	}
>  
>  	/* Init tDma */
> -	bcmgenet_tdma_writel(priv, DMA_MAX_BURST_LENGTH, DMA_SCB_BURST_SIZE);
> +	bcmgenet_tdma_writel(priv, priv->dma_max_burst_length,
> +			     DMA_SCB_BURST_SIZE);
>  
>  	/* Initialize Tx queues */
>  	bcmgenet_init_tx_queues(priv->dev);
> @@ -3522,6 +3524,13 @@ static int bcmgenet_probe(struct platform_device *pdev)
>  
>  	clk_prepare_enable(priv->clk);
>  
> +	if (dn) {
> +		of_property_read_u32(dn, "dma-burst-sz",
> +				     &priv->dma_max_burst_length);

You set the 'dma-burst-sz' binding as optional, though this assumes that if a
device node is available dma_max_burst_length comes from the device tree. I
think you should check of_property_read_u32's return value and on failure
default to DMA_MAX_BURST_LENGTH.

> +	} else {
> +		priv->dma_max_burst_length = DMA_MAX_BURST_LENGTH;
> +	}
> +
>  	bcmgenet_set_hw_params(priv);
>  
>  	/* Mii wait queue */
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> index 4a8fc03d82fd..897f356eb376 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> @@ -663,6 +663,7 @@ struct bcmgenet_priv {
>  	bool crc_fwd_en;
>  
>  	unsigned int dma_rx_chk_bit;
> +	unsigned int dma_max_burst_length;
>  
>  	u32 msg_enable;
>  

Regards,
Nicolas