netdev - Re: [RFC 07/12] ravb: Fillup ravb_rx

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Date:   Thu, 7 Oct 2021 22:04:40 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Biju Das <biju.das.jz@...renesas.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
CC:     Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Sergey Shtylyov <s.shtylyov@...russia.ru>,
        "Adam Ford" <aford173@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Yuusuke Ashizuka <ashiduka@...itsu.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [RFC 07/12] ravb: Fillup ravb_rx_gbeth() stub

On 10/7/21 8:49 AM, Biju Das wrote:

[...]
>>>>> Fillup ravb_rx_gbeth() function to support RZ/G2L.
>>>>>
>>>>> This patch also renames ravb_rcar_rx to ravb_rx_rcar to be
>>>>> consistent with the naming convention used in sh_eth driver.
>>>>>
>>>>> Signed-off-by: Biju Das <biju.das.jz@...renesas.com>
>>>>> Reviewed-by: Lad Prabhakar
>>>>> <prabhakar.mahadev-lad.rj@...renesas.com>[...]
>>>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c
>>>>> b/drivers/net/ethernet/renesas/ravb_main.c
>>>>> index 37164a983156..42573eac82b9 100644
>>>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>>>>> @@ -720,6 +720,23 @@ static void ravb_get_tx_tstamp(struct
>>>>> net_device
>>>> *ndev)
>>>>>  	}
>>>>>  }
>>>>>
>>>>> +static void ravb_rx_csum_gbeth(struct sk_buff *skb) {
>>>>> +	u8 *hw_csum;
>>>>> +
>>>>> +	/* The hardware checksum is contained in sizeof(__sum16) (2) bytes
>>>>> +	 * appended to packet data
>>>>> +	 */
>>>>> +	if (unlikely(skb->len < sizeof(__sum16)))
>>>>> +		return;
>>>>> +	hw_csum = skb_tail_pointer(skb) - sizeof(__sum16);
>>>>
>>>>    Not 32-bit? The manual says the IP checksum is stored in the first
>>>> 2 bytes.
>>>
>>> It is 16 bit. It is on last 2 bytes.

   The IP checksum is at the 1st 2 bytes of the overall 4-byte checksum (coming after
the packet payload), no?

>>    So you're saying the manual is wrong?
> 
> I am not sure which manual you are referring here.
> 
> I am referring to Rev.1.00 Sep, 2021 of RZ/G2L hardware manual and

   Same here.

[...]

> Please check the section 30.5.6.1 checksum calculation handling> And figure 30.25 the field of checksum attaching field

   I have.

> Also see Table 30.17 for checksum values for non-error conditions.

> TCP/UDP/ICPM checksum is at last 2bytes.

   What are you arguing with then? :-)
   My point was that your code fetched the TCP/UDP/ICMP checksum ISO the IP checksum
because it subtracts sizeof(__sum16), while should probably subtract sizeof(__wsum).

>>>>> +
>>>>> +	if (*hw_csum == 0)
>>>>
>>>>    You only check the 1st byte, not the full checksum!
>>>
>>> As I said earlier, "0" value on last 16 bit, means no checksum error.
>>
>>    How's that? 'hw_csum' is declared as 'u8 *'!
> 
> It is my mistake, which will be taken care in the next patch by using u16 *.

   Note that this 'u16' halfword can be unaligned, that's why the current code uses get_unaligned_le16().

>>>>> +		skb->ip_summed = CHECKSUM_UNNECESSARY;
>>>>> +	else
>>>>> +		skb->ip_summed = CHECKSUM_NONE;
>>>>
>>>>   So the TCP/UDP/ICMP checksums are not dealt with? Why enable them
>> then?
>>>
>>> If last 2bytes is zero, means there is no checksum error w.r.to
>> TCP/UDP/ICMP checksums.
>>
>>    Why checksum them independently then?
> 
> It is a hardware feature. 

   Switchable, isn't it?

> Regards,
> Biju

[...]

MBR, Sergey