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

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Message-ID: <bfb2ebd9-0d96-4ce2-b766-358c7253e065@omp.ru>
Date: Thu, 3 Oct 2024 16:20:01 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul.barker.ct@...renesas.com>, 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: 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 10/3/24 12:23, Paul Barker 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)
>>>  	 * The last 2 bytes are the protocol checksum status which will be zero
>>>  	 * if the checksum has been validated.
>>>  	 */
>>> -	if (unlikely(skb->len < sizeof(__sum16) * 2))
>>> +	csum_len = sizeof(*hw_csum) * 2;
>>
>>    Could've been done by an initializer instead?
> 
> So, if I move this to the initializers at the start of the function,
> csum_len must be declared after hw_csum which breaks reverse Christmas
> tree ordering:
> 
>     struct skb_shared_info *shinfo = skb_shinfo(skb);
>     u16 *hw_csum;
>     size_t csum_len = sizeof(*hw_csum) * 2;

   Could use sizeof(u16) instead, but it's OK to ignore me on this
matter. :-)

> Thanks,

MBR, Sergey