netdev - Re: [net] cxgb4: advertise NETIF_F_HW

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Date:   Wed, 6 Jan 2021 09:39:57 +0200
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Rohit Maheshwari <rohitm@...lsio.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, secdev@...lsio.com,
        Tariq Toukan <tariqt@...dia.com>,
        Boris Pismenny <borisp@...dia.com>
Subject: Re: [net] cxgb4: advertise NETIF_F_HW_CSUM

On 1/5/2021 10:29 PM, Jakub Kicinski wrote:
> On Tue,  5 Jan 2021 22:27:49 +0530 Rohit Maheshwari wrote:
>> advertise NETIF_F_HW_CSUM instead of protocol specific values of
>> NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM. This change is added long
>> back in other drivers. This issue is seen recently when TLS offload
>> made it mandatory to enable NETIF_F_HW_CSUM.
>>
>> Fixes: 2ed28baa7076 ("net: cxgb4{,vf}: convert to hw_features")
>> Signed-off-by: Rohit Maheshwari <rohitm@...lsio.com>
> 
> Ugh, commit ae0b04b238e2 ("net: Disable NETIF_F_HW_TLS_TX when HW_CSUM
> is disabled") is buggy, it should probably use NETIF_F_CSUM_MASK.
> Can you fix that instead?
> 

The HW_TLS_TX feature is for both IPv4/6. We do not want to allow 
NETIF_F_HW_TLS_TX if only one of (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM) 
is set (of course NETIF_F_HW_CSUM is not set in this case).
Hence, using NETIF_F_CSUM_MASK would not be a strong enough condition.

I think we have two options here:
Either (1) request device drivers to move to NETIF_F_HW_CSUM if they 
want to have HW_TLS_TX (as it is today), or (2) use the following condition:
((features & NETIF_F_IP_CSUM) && (features & NETIF_F_IPV6_CSUM)) || 
(features & NETIF_F_HW_CSUM).

Thanks,
Tariq