netdev - Re: [net-next PATCH 05/11] net: ravb: Simplify types in RX csum validation

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Message-ID: <8cb1de35-a40a-4d1b-a081-1b8fc08e0a6a@omp.ru>
Date: Mon, 30 Sep 2024 22:30:25 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul@...rker.dev>, "David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>
CC: Paul Barker <paul.barker.ct@...renesas.com>, Geert Uytterhoeven
	<geert+renesas@...der.be>, Niklas Söderlund
	<niklas.soderlund+renesas@...natech.se>, Biju Das
	<biju.das.jz@...renesas.com>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>, <netdev@...r.kernel.org>,
	<linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [net-next PATCH 05/11] net: ravb: Simplify types in RX csum
 validation

On 9/30/24 22:11, Sergey Shtylyov wrote:
[...]

>> From: Paul Barker <paul.barker.ct@...renesas.com>
>>
>> The HW checksum value is used as a 16-bit flag, it is zero when the
> 
>    I think I prefer s/HW/hardware/ but there's no hard feelings... :-)
> 
>> checksum has been validated and non-zero otherwise. Therefore we don't
>> need to treat this as an actual __wsum type or call csum_unfold(), we
>> can just use a u16 pointer.
>>
>> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
> [...]
>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>> index 1dd2152734b0..9350ca10ab22 100644
>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> [...]
>> @@ -762,23 +761,22 @@ static void ravb_rx_csum_gbeth(struct sk_buff *skb)
[...]
>> +	if (unlikely(skb->len < csum_len))
>>  		return;
>>  
>>  	if (skb_is_nonlinear(skb)) {
>> -		last_frag = &shinfo->frags[shinfo->nr_frags - 1];
>> -		hw_csum = skb_frag_address(last_frag) +
>> -			  skb_frag_size(last_frag);
>> -		skb_frag_size_sub(last_frag, 2 * sizeof(__sum16));
>> +		skb_frag_t *last_frag = &shinfo->frags[shinfo->nr_frags - 1];
> 
>    Could've been done in the previous patch...

   Even fit better there, I think...

>> +
>> +		hw_csum = (u16 *)(skb_frag_address(last_frag) +
>> +				  skb_frag_size(last_frag));
>> +		skb_frag_size_sub(last_frag, csum_len);
>>  	} else {
>> -		hw_csum = skb_tail_pointer(skb);
>> -		skb_trim(skb, skb->len - 2 * sizeof(__sum16));
>> +		hw_csum = (u16 *)skb_tail_pointer(skb);
>> +		skb_trim(skb, skb->len - csum_len);
>>  	}
>>  
>> -	hw_csum -= sizeof(__sum16);
>> -	csum_proto = csum_unfold((__force __sum16)get_unaligned_le16(hw_csum));
>> -
>> -	if (!csum_proto)
>> +	if (!*--hw_csum)
> 
>    Hm, you lost get_unaligned_le16() here. The checksum can be anywhere,
> unaligned too...

   No need to keep using get_unaligned_le16() itself but you should then switch to 
using get_unaligned().

[...]

MBR, Sergey