netdev - Re: [PATCH net-next 5/8] net: lantiq: configure the burst length in ethernet drivers

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Date:   Wed, 15 Sep 2021 00:36:37 +0200
From:   Hauke Mehrtens <hauke@...ke-m.de>
To:     Aleksander Jan Bajkowski <olek2@...pl>, john@...ozen.org,
        tsbogend@...ha.franken.de, maz@...nel.org, ralf@...ux-mips.org,
        ralph.hempel@...tiq.com, davem@...emloft.net, kuba@...nel.org,
        robh+dt@...nel.org, dev@...sin.me, arnd@...db.de, jgg@...pe.ca,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 5/8] net: lantiq: configure the burst length in
 ethernet drivers

On 9/14/21 11:21 PM, Aleksander Jan Bajkowski wrote:
> Configure the burst length in Ethernet drivers. This improves
> Ethernet performance by 58%. According to the vendor BSP,
> 8W burst length is supported by ar9 and newer SoCs.
> 
> The NAT benchmark results on xRX200 (Down/Up):
> * 2W: 330 Mb/s
> * 4W: 432 Mb/s    372 Mb/s
> * 8W: 520 Mb/s    389 Mb/s
> 
> Tested on xRX200 and xRX330.
> 
> Signed-off-by: Aleksander Jan Bajkowski <olek2@...pl>
> ---
>   drivers/net/ethernet/lantiq_etop.c   | 21 ++++++++++++++++++---
>   drivers/net/ethernet/lantiq_xrx200.c | 21 ++++++++++++++++++---
>   2 files changed, 36 insertions(+), 6 deletions(-)
> 
.....
> diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
> index fb78f17d734f..5d96248ce83b 100644
> --- a/drivers/net/ethernet/lantiq_xrx200.c
> +++ b/drivers/net/ethernet/lantiq_xrx200.c
> @@ -71,6 +71,9 @@ struct xrx200_priv {
>   	struct net_device *net_dev;
>   	struct device *dev;
>   
> +	int tx_burst_len;
> +	int rx_burst_len;
> +
>   	__iomem void *pmac_reg;
>   };
>   
> @@ -316,8 +319,8 @@ static netdev_tx_t xrx200_start_xmit(struct sk_buff *skb,
>   	if (unlikely(dma_mapping_error(priv->dev, mapping)))
>   		goto err_drop;
>   
> -	/* dma needs to start on a 16 byte aligned address */
> -	byte_offset = mapping % 16;
> +	/* dma needs to start on a burst length value aligned address */
> +	byte_offset = mapping % (priv->tx_burst_len * 4);
>   
>   	desc->addr = mapping - byte_offset;
>   	/* Make sure the address is written before we give it to HW */
> @@ -369,7 +372,7 @@ static int xrx200_dma_init(struct xrx200_priv *priv)
>   	int ret = 0;
>   	int i;
>   
> -	ltq_dma_init_port(DMA_PORT_ETOP);
> +	ltq_dma_init_port(DMA_PORT_ETOP, priv->tx_burst_len, rx_burst_len);
>   
>   	ch_rx->dma.nr = XRX200_DMA_RX;
>   	ch_rx->dma.dev = priv->dev;
> @@ -478,6 +481,18 @@ static int xrx200_probe(struct platform_device *pdev)
>   	if (err)
>   		eth_hw_addr_random(net_dev);
>   
> +	err = device_property_read_u32(dev, "lantiq,tx-burst-length", &priv->tx_burst_len);
> +	if (err < 0) {
> +		dev_err(dev, "unable to read tx-burst-length property\n");
> +		return err;
> +	}
> +
> +	err = device_property_read_u32(dev, "lantiq,rx-burst-length", &priv->rx_burst_len);
> +	if (err < 0) {
> +		dev_err(dev, "unable to read rx-burst-length property\n");
> +		return err;
> +	}
> +

I would prefer if you would hard code these values to 8 for the xrx200 
driver. All SoCs with this IP block should support this.

>   	/* bring up the dma engine and IP core */
>   	err = xrx200_dma_init(priv);
>   	if (err)
> 

Hauke