netdev - Re: [PATCH net-next 08/19] net: usb: aqc111: Implement TX data path

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Date:   Sat, 6 Oct 2018 03:13:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Igor Russkikh <Igor.Russkikh@...antia.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Dmitry Bezrukov <Dmitry.Bezrukov@...antia.com>
Subject: Re: [PATCH net-next 08/19] net: usb: aqc111: Implement TX data path

> +static struct sk_buff *aqc111_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
> +				       gfp_t flags)
> +{
> +	struct aq_tx_packet_desc tx_hdr;
> +	int frame_size = dev->maxpacket;
> +	int headroom = 0;
> +	int tailroom = 0;
> +	int padding_size = 0;
> +	struct sk_buff *new_skb = NULL;
> +
> +	memset(&tx_hdr, 0x00, sizeof(tx_hdr));
> +
> +	/*Length of actual data*/
> +	tx_hdr.length = (skb->len & 0x1FFFFF);
> +
> +	headroom = (skb->len + AQ_TX_HEADER_SIZE) % 8;
> +	if (headroom != 0)
> +		padding_size = 8 - headroom;
> +
> +	if (((skb->len + AQ_TX_HEADER_SIZE + padding_size) % frame_size) == 0) {
> +		padding_size += 8;
> +		tx_hdr.drop_padding = 1;
> +	}
> +
> +	if (!dev->can_dma_sg && (dev->net->features & NETIF_F_SG) &&
> +	    skb_linearize(skb))
> +		return NULL;
> +
> +	headroom = skb_headroom(skb);
> +	tailroom = skb_tailroom(skb);
> +
> +	if (!(headroom >= AQ_TX_HEADER_SIZE && tailroom >= padding_size)) {
> +		new_skb = skb_copy_expand(skb, AQ_TX_HEADER_SIZE,
> +					  padding_size, flags);
> +		dev_kfree_skb_any(skb);
> +		skb = new_skb;
> +		if (!skb)
> +			return NULL;
> +	}
> +	if (padding_size != 0)
> +		skb_put(skb, padding_size);
> +	/* Copy TX header */
> +	skb_push(skb, AQ_TX_HEADER_SIZE);
> +	cpu_to_le64s(&tx_hdr);

Is that portable? tx_hdr is a structure of 2x u32 bitfields.  What
endian have you tested that one?

> +	skb_copy_to_linear_data(skb, &tx_hdr, 8);
> +
> +	usbnet_set_skb_tx_stats(skb, 1, 0);
> +
> +	return skb;
> +}

> +struct aq_tx_packet_desc {
> +	struct {
> +		u32 length:21;
> +		u32 checksum:7;
> +		u32 drop_padding:1;
> +		u32 vlan_tag:1;
> +		u32 cphi:1;
> +		u32 dicf:1;
> +	};
> +	struct {
> +		u32 max_seg_size:15;
> +		u32 reserved:1;
> +		u32 vlan_info:16;
> +	};
> +};

  Andrew