netdev - Re: [PATCH net-next v2 8/9] net: rswitch: Add jumbo frames handling for TX

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Date: Fri, 1 Dec 2023 11:54:47 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH net-next v2 8/9] net: rswitch: Add jumbo frames handling
 for TX

On 12/1/23 8:46 AM, Yoshihiro Shimoda wrote:

> If the driver would like to transmit a jumbo frame like 2KiB or more,
> it should be split into multiple queues. In the near future, to support
> this, add handling specific descriptor types F{START,MID,END}. However,
> such jumbo frames will not happen yet because the maximum MTU size is
> still default for now.
> 
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
[...]

> diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
> index 009e6bfdad27..c5e3ee8f82bc 100644
> --- a/drivers/net/ethernet/renesas/rswitch.c
> +++ b/drivers/net/ethernet/renesas/rswitch.c
> @@ -1631,15 +1631,44 @@ static bool rswitch_ext_desc_set(struct rswitch_device *rdev,
[...]
>  static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  {
>  	struct rswitch_device *rdev = netdev_priv(ndev);
>  	struct rswitch_gwca_queue *gq = rdev->tx_queue;
> +	dma_addr_t dma_addr, dma_addr_orig;
>  	netdev_tx_t ret = NETDEV_TX_OK;
>  	struct rswitch_ext_desc *desc;
> -	dma_addr_t dma_addr;
> +	unsigned int i, nr_desc;
> +	u8 die_dt;
> +	u16 len;
>  
> -	if (rswitch_get_num_cur_queues(gq) >= gq->ring_size - 1) {
> +	nr_desc = (skb->len - 1) / RSWITCH_DESC_BUF_SIZE + 1;
> +	if (rswitch_get_num_cur_queues(gq) >= gq->ring_size - nr_desc) {
>  		netif_stop_subqueue(ndev, 0);
>  		return NETDEV_TX_BUSY;
>  	}
> @@ -1647,19 +1676,26 @@ static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *nd
>  	if (skb_put_padto(skb, ETH_ZLEN))
>  		return ret;
>  
> -	dma_addr = dma_map_single(ndev->dev.parent, skb->data, skb->len, DMA_TO_DEVICE);
> +	dma_addr_orig = dma_map_single(ndev->dev.parent, skb->data, skb->len, DMA_TO_DEVICE);
>  	if (dma_mapping_error(ndev->dev.parent, dma_addr))

   Not dma_addr_orig? dma_addr isn't even set at this point, no?

[...]

MBR, Sergey