From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Date: Fri, 18 Oct 2019 10:34:57 +1100 Subject: [PATCH v2] ftgmac100: Disable HW checksum generation on AST2500 In-Reply-To: <071cf1eeefcbfc14633a13bc2d15ad7392987a88.camel@kernel.crashing.org> References: <20191011213027.2110008-1-vijaykhemka@fb.com> <3a1176067b745fddfc625bbd142a41913ee3e3a1.camel@kernel.crashing.org> <0C0BC813-5A84-403F-9C48-9447AAABD867@fb.com> <071cf1eeefcbfc14633a13bc2d15ad7392987a88.camel@kernel.crashing.org> Message-ID: List-Id: To: linux-aspeed@lists.ozlabs.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, 2019-10-18 at 10:14 +1100, Benjamin Herrenschmidt wrote: > > 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. > > 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. I did get that piece of information from Aspeed: The HW checksum generation is supported if: - The length of UDP header is always 20 bytes. - The length of TCP and IP header have 4 * N bytes (N is 5 to 15). Now these afaik are also the protocol limits, so it *should* work. Or am I missing something or some funky encaspulation/header format that can be used under some circumstances ? Cheers, Ben.