Messages in this thread Patch in this message | | | From | Vijay Khemka <> | Subject | Re: [PATCH v2] ftgmac100: Disable HW checksum generation on AST2500 | Date | Fri, 18 Oct 2019 22:50:32 +0000 |
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On 10/17/19, 5:33 PM, "Benjamin Herrenschmidt" <benh@kernel.crashing.org> wrote:
On Fri, 2019-10-18 at 00:06 +0000, Vijay Khemka wrote: > > > This is not a matter of unsupported csum, it is broken hw csum. > > That's why we disable hw checksum. My guess is once we disable > > Hw checksum, it will use sw checksum. So I am just disabling hw > > Checksum. > > I don't understand what you are saying. You reported a problem with > IPV6 checksums generation. The HW doesn't support it. What's "not a > matter of unsupported csum" ? > > Your patch uses a *deprecated* bit to tell the network stack to only do > HW checksum generation on IPV4. > > This bit is deprecated for a reason, again, see skbuff.h. The right > approach, *which the driver already does*, is to tell the stack that we > support HW checksuming using NETIF_F_HW_CSUM, and then, in the transmit > handler, to call skb_checksum_help() to have the SW calculate the > checksum if it's not a supported type. > > My understanding was when we enable NETIF_F_HW_CSUM means network > stack enables HW checksum and doesn't calculate SW checksum. But as per > this supported types HW checksum are used only for IPV4 and not for IPV6 even > though driver enabled NETIF_F_HW_CSUM. For IPV6 it is always a SW generated > checksum, please correct me here. Have you actually read the comments in skbuff.h that I pointed you to ? And the rest of my email for that matter ?
Yes, I went through comments in skbuff.h and your comments as well. I knew about this deprecated bit that's why I have disabled NETIF_F_HW_CSUM completely in my V1 patch. Then Florian gave a comment and asked me to disable only IPV6 not IPV4 as it is working for IPV4 and issue with only IPV6. That's why I sent patch V2 accommodating his feedback.
I don't have much understanding of IP Stack but I went through code details and you are right and found that it should fallback to SW calculation for IPV6 but it doesn't happen because ftgmac100_hard_start_xmit checks for CHECKSUM_PARTIAL before setting HW checksum and calling ftgmac100_prep_tx_csum function. And in my understanding, this value is set CHECKSUM_PARTIAL in IP stack. I looked up IP stack for IPV6, file net/ipv6/ip6_output.c, function __ip6_append_data: here it sets CHECKSUM_PARTIAL only for UDP packets not for TCP packets. Please look at line number 1880. This could be an issue we are seeing here as why ftgmac100_prep_tx_csum is not getting triggered for IPV6 with TCP. Please correct me if my understanding is wrong. > This is exactly what ftgmac100_prep_tx_csum() does. It only enables HW > checksum generation on supported types and uses skb_checksum_help() > otherwise, supported types being protocol ETH_P_IP and IP protocol > being raw IP, TCP and UDP. > > > So this *should* have fallen back to SW for IPV6. So either something > in my code there is making an incorrect assumption, or something is > broken in skb_checksum_help() for IPV6 (which I somewhat doubt) or > something else I can't think of, but setting a *deprecated* flag is > definitely not the right answer, neither is completely disabling HW > checksumming. > > So can you investigate what's going on a bit more closely please ? I > can try myself, though I have very little experience with IPV6 and > probably won't have time before next week. > > Cheers, > Ben. > > > The driver should have handled unsupported csum via SW fallback > > already in ftgmac100_prep_tx_csum() > > > > Can you check why this didn't work for you ? > > > > Cheers, > > Ben. > > > > > Signed-off-by: Vijay Khemka <vijaykhemka@fb.com> > > > --- > > > Changes since v1: > > > Enabled IPV4 hw checksum generation as it works for IPV4. > > > > > > drivers/net/ethernet/faraday/ftgmac100.c | 13 ++++++++++++- > > > 1 file changed, 12 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/net/ethernet/faraday/ftgmac100.c > > > b/drivers/net/ethernet/faraday/ftgmac100.c > > > index 030fed65393e..0255a28d2958 100644 > > > --- a/drivers/net/ethernet/faraday/ftgmac100.c > > > +++ b/drivers/net/ethernet/faraday/ftgmac100.c > > > @@ -1842,8 +1842,19 @@ static int ftgmac100_probe(struct > > > platform_device *pdev) > > > /* AST2400 doesn't have working HW checksum generation */ > > > if (np && (of_device_is_compatible(np, "aspeed,ast2400-mac"))) > > > netdev->hw_features &= ~NETIF_F_HW_CSUM; > > > + > > > + /* AST2500 doesn't have working HW checksum generation for IPV6 > > > + * but it works for IPV4, so disabling hw checksum and enabling > > > + * it for only IPV4. > > > + */ > > > + if (np && (of_device_is_compatible(np, "aspeed,ast2500-mac"))) > > > { > > > + netdev->hw_features &= ~NETIF_F_HW_CSUM; > > > + netdev->hw_features |= NETIF_F_IP_CSUM; > > > + } > > > + > > > if (np && of_get_property(np, "no-hw-checksum", NULL)) > > > - netdev->hw_features &= ~(NETIF_F_HW_CSUM | > > > NETIF_F_RXCSUM); > > > + netdev->hw_features &= ~(NETIF_F_HW_CSUM | > > > NETIF_F_RXCSUM > > > + | NETIF_F_IP_CSUM); > > > netdev->features |= netdev->hw_features; > > > > > > /* register network device */ > > > > > > > > >
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