RE: [RFC 07/12] ravb: Fillup ravb_rx_gbeth() stub

[Biju Das <biju.das.jz@bp.renesas.com>]

Hi Sergey,

> Subject: RE: [RFC 07/12] ravb: Fillup ravb_rx_gbeth() stub
> 
> Hi Sergey,
> 
> 
> Thanks for the feedback.
> 
> > 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@bp.renesas.com>
> > >>>>> Reviewed-by: Lad Prabhakar
> > >>>>> <prabhakar.mahadev-lad.rj@bp.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?
> 
> Sorry, I got confused with your question earlier. Now it is clear for me.
> 
> I agree the checksum part is stored in last 4bytes. Of this, the first 2
> bytes IPV4 checksum and last 2 bytes TCP/UDP/ICMP checksum.
> 
> >
> > >>    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)
> 
> Agreed. My code missed IP4 checksum result. May be we need to extract 2
> checksum info from last 4 bytes.  First checksum(2bytes) is IP4 header
> checksum and next checksum(2 bytes)  for TCP/UDP/ICMP and use this info
> finding the non error case mentioned in  Table 30.17.
> 
> For eg:-
> IPV6 non error-condition -->  "0xFFFF"-->IPV4HeaderCSum value and "0x0000"
> TCP/UDP/ICMP CSUM value
> 
> IPV4 non error-condition -->  "0x0000"-->IPV4HeaderCSum value and "0x0000"
> TCP/UDP/ICMP CSUM value
> 
> Do you agree?

What I meant here is some thing like below, please let me know if you have any issues with
this, otherwise I would like to send the patch with below changes.

Further improvements can happen later.

Please let me know.

+/* Hardware checksum status */
+#define IPV4_RX_CSUM_OK                0x00000000
+#define IPV6_RX_CSUM_OK                0xFFFF0000
+
 enum ravb_reg {
        /* AVB-DMAC registers */
        CCC     = 0x0000,
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index bbb42e5328e4..d9201fbbd472 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -722,16 +722,18 @@ static void ravb_get_tx_tstamp(struct net_device *ndev)
 
 static void ravb_rx_csum_gbeth(struct sk_buff *skb)
 {
-       u16 *hw_csum;
+       u32 csum_result;
+       u8 *hw_csum;
 
        /* The hardware checksum is contained in sizeof(__sum16) (2) bytes
         * appended to packet data
         */
-       if (unlikely(skb->len < sizeof(__sum16)))
+       if (unlikely(skb->len < sizeof(__wsum)))
                return;
-       hw_csum = (u16*)(skb_tail_pointer(skb) - sizeof(__sum16));
+       hw_csum = skb_tail_pointer(skb) - sizeof(__wsum);
+       csum_result = get_unaligned_le32(hw_csum);
 
-       if (*hw_csum == 0)
+       if (csum_result == IPV4_RX_CSUM_OK || csum_result == IPV6_RX_CSUM_OK)

Regards,
Biju

> 
> Regards,
> Biju
> >
> > >>>>> +
> > >>>>> +	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