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

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Date:   Thu, 7 Oct 2021 05:49:09 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Sergey Shtylyov <s.shtylyov@....ru>,
        "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

Hi Sergey,

> Subject: Re: [RFC 07/12] ravb: Fillup ravb_rx_gbeth() stub
> 
> On 10/6/21 11:22 PM, 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.
> 
>    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
I have shared the link[1] for you to download. Hope you are referring same manual


[1] https://www.renesas.com/document/mah/rzg2l-group-rzg2lc-group-users-manual-hardware-0?language=en&r=1467981

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

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

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

> 
> >>
> >>> +
> >>> +	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 *.

> 
> >>> +		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. 

Regards,
Biju

> 
> > RZ/G2L checksum part is different from R-Car Gen3. There is no TOE block
> at all for R-Car Gen3.
> >
> > Regards,
> > Biju
> 
> [...]
> 
> MBR, Sergey