Re: [PATCH 11/11] net: xilinx: Show csum in bootlog

From: Michal Simek <monstr@monstr.eu>
To: Ben Hutchings <bhutchings@solarflare.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Anirudha Sarangi <anirudh@xilinx.com>,
	John Linn <John.Linn@xilinx.com>,
	Grant Likely <grant.likely@secretlab.ca>,
	Rob Herring <rob.herring@calxeda.com>,
	"David S. Miller" <davem@davemloft.net>,
	John Linn <linnj@xilinx.com>
Subject: Re: [PATCH 11/11] net: xilinx: Show csum in bootlog
Date: Wed, 10 Oct 2012 18:06:05 +0200	[thread overview]
Message-ID: <CAHTX3dJuHxAqZOkkSymPz5ots1Edq4ty3o1rGAuhnpWrUwtWZQ@mail.gmail.com> (raw)
In-Reply-To: <1349801800.2800.21.camel@bwh-desktop.uk.solarflarecom.com>

2012/10/9 Ben Hutchings <bhutchings@solarflare.com>:
> On Tue, 2012-10-09 at 11:08 +0200, Michal Simek wrote:
>> On 10/05/2012 03:51 PM, Ben Hutchings wrote:
>> > On Fri, 2012-10-05 at 11:35 +0200, Michal Simek wrote:
>> >> On 10/04/2012 09:15 PM, Ben Hutchings wrote:
>> >>> On Thu, 2012-10-04 at 20:14 +0200, Michal Simek wrote:
>> >>>> Just show current setting in bootlog.
>> >>> [...]
>> >>>> --- a/drivers/net/ethernet/xilinx/ll_temac_main.c
>> >>>> +++ b/drivers/net/ethernet/xilinx/ll_temac_main.c
>> >>>> @@ -1052,12 +1052,14 @@ static int __devinit temac_of_probe(struct platform_device *op)
>> >>>>          /* Setup checksum offload, but default to off if not specified */
>> >>>>          lp->temac_features = 0;
>> >>>>          p = (__be32 *)of_get_property(op->dev.of_node, "xlnx,txcsum", NULL);
>> >>>> +        dev_info(&op->dev, "TX_CSUM %d\n", be32_to_cpup(p));
>> >>>>          if (p && be32_to_cpu(*p)) {
>> >>>>                  lp->temac_features |= TEMAC_FEATURE_TX_CSUM;
>> >>>>                  /* Can checksum TCP/UDP over IPv4. */
>> >>>>                  ndev->features |= NETIF_F_IP_CSUM;
>> >>>>          }
>> >>>>          p = (__be32 *)of_get_property(op->dev.of_node, "xlnx,rxcsum", NULL);
>> >>>> +        dev_info(&op->dev, "RX_CSUM %d\n", be32_to_cpup(p));
>> >>> [...]
>> >>>
>> >>> Is there any particular reason you think this needs to be logged by
>> >>> default, rather than letting users run ethtool -k?  I suggest using
>> >>> dev_dbg() instead.
>> >>
>> >> Ok. I have looked at it and there are missing some bits in ndev->features.
>> >>
>> >> Can you please check that my setting is correct?
>> >>
>> >> It is SG DMA ip/driver.
>> >> ndev->features = NETIF_F_FRAGLIST | NETIF_F_SG
>> >
>> > NETIF_F_SG only; NETIF_F_FRAGLIST means you can handle skbs chained
>> > through the frag_list pointer.
>>
>> The driver is able to handle skb fragments too. temac_start_xmit
>
> "git grep -w -E 'frag_list|skb_walk_frags|skb_to_sgvec' drivers/net/ethernet/xilinx"
> returns nothing in net-next.

What about this? Maybe it is different fragmentation.
drivers/net/ethernet/xilinx/ll_temac_main.c
 688         num_frag = skb_shinfo(skb)->nr_frags;
 689         frag = &skb_shinfo(skb)->frags[0];

>
> [...]
>> >> rx Full csum -> NETIF_F_RXCSUM
>> >>
>> >> Is there any option to support partial csum?
>> >
>> > There is no need to differentiate these in the device features.  For TX
>> > the stack needs to know whether to use a software fallback before
>> > passing the skb to you, but on RX it looks at the ip_summed field of
>> > each skb you pass up.
>>
>> Hardware can be setup asymmetrically. It means enable CSUM only on RX or TX.
>> All combination are valid.
>> The point here is if Linux is not able to handle this then we have to
>> create logic in the driver to support these options too.
>
> Linux handles this just fine.  The point is you don't have to tell the
> stack in advance whether or what kind of RX checksum validation your
> devices will do.  (In fact the only reason that feature flag exists at
> all is so that it can be generically exposed through the ethtool API.)

Ok.

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian