linux-kernel - Re: [PATCH net-next v3 3/7] net: lan966x: Add len field to lan966x_tx_dcb

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Date:   Tue, 22 Nov 2022 12:30:22 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next v3 3/7] net: lan966x: Add len field to lan966x_tx_dcb_buf

From: Horatiu Vultur <horatiu.vultur@...rochip.com>
Date: Mon, 21 Nov 2022 22:28:46 +0100

> Currently when a frame was transmitted, it is required to unamp the
> frame that was transmitted. The length of the frame was taken from the
> transmitted skb. In the future we might not have an skb, therefore store
> the length skb directly in the lan966x_tx_dcb_buf and use this one to
> unamp the frame.
> 
> Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> ---
>  drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c | 5 +++--
>  drivers/net/ethernet/microchip/lan966x/lan966x_main.h | 1 +
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> index 94c720e59caee..384ed34197d58 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> @@ -391,12 +391,12 @@ static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
>  			continue;
>  
>  		dcb_buf->dev->stats.tx_packets++;
> -		dcb_buf->dev->stats.tx_bytes += dcb_buf->skb->len;
> +		dcb_buf->dev->stats.tx_bytes += dcb_buf->len;
>  
>  		dcb_buf->used = false;
>  		dma_unmap_single(lan966x->dev,
>  				 dcb_buf->dma_addr,
> -				 dcb_buf->skb->len,
> +				 dcb_buf->len,
>  				 DMA_TO_DEVICE);
>  		if (!dcb_buf->ptp)
>  			dev_kfree_skb_any(dcb_buf->skb);
> @@ -709,6 +709,7 @@ int lan966x_fdma_xmit(struct sk_buff *skb, __be32 *ifh, struct net_device *dev)
>  	/* Fill up the buffer */
>  	next_dcb_buf = &tx->dcbs_buf[next_to_use];
>  	next_dcb_buf->skb = skb;
> +	next_dcb_buf->len = skb->len;
>  	next_dcb_buf->dma_addr = dma_addr;
>  	next_dcb_buf->used = true;
>  	next_dcb_buf->ptp = false;
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> index bc93051aa0798..7bb9098496f60 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> @@ -175,6 +175,7 @@ struct lan966x_rx {
>  struct lan966x_tx_dcb_buf {
>  	struct net_device *dev;
>  	struct sk_buff *skb;
> +	int len;

Nit: perhaps you can define it as `u32` since fram length can't be
negative?

>  	dma_addr_t dma_addr;

Oh, also, on platforms with 64-bit addressing, `int len` placed in
between ::skb and ::dma_addr would create a 4-byte hole in the
structure. Placing `len` after ::dma_addr would make it holeless on
any architercture.

>  	bool used;
>  	bool ptp;
> -- 
> 2.38.0

Thanks,
Olek