netdev - Re: [Linux-kernel] [PATCH 3/4] usbnet: smsc95xx: check for csum being in last four bytes

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Message-ID: <1538672124.3024.270.camel@codethink.co.uk>
Date:   Thu, 04 Oct 2018 17:55:24 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>, netdev@...r.kernel.org
Cc:     linux-kernel@...ts.codethink.co.uk, linux-usb@...r.kernel.org,
        oneukum@...e.com, linux-kernel@...r.kernel.org, davem@...emloft.net
Subject: Re: [Linux-kernel] [PATCH 3/4] usbnet: smsc95xx: check for csum
 being in last four bytes

On Tue, 2018-10-02 at 10:26 +0100, Ben Dooks wrote:
[...]
> @@ -2031,7 +2045,8 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
> >  	}
>  
>  	if (csum) {
> -		if (skb->len <= 45) {
> +		/* note, csum does not work if csum in last DWORD of packet */
> +		if (skb->len <= 45 || !smsc95xx_can_checksum(skb)) {

It would make more sense to move the length check into
smsc95xx_can_checksum() as well.

Ben.

>  			/* workaround - hardware tx checksum does not work
>  			 * properly with extremely small packets */
>  			long csstart = skb_checksum_start_offset(skb);
-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom