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:

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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
[off-list ref][...]

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)

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 	}
 }

+static void ravb_rx_csum_gbeth(struct sk_buff *skb) {
+	u8 *hw_csum;
+
+	/* The hardware checksum is contained in sizeof(__sum16) (2)

bytes

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+	 * 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.

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   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.

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

   I have.

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

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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?

Regards,
Biju

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+
+	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().

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+		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?

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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?

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Regards,
Biju

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MBR, Sergey