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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Andrew Lunn <andrew@lunn.ch>, wei.fang@nxp.com
Cc:     davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com, ast@kernel.org, daniel@iogearbox.net,
        hawk@kernel.org, john.fastabend@gmail.com, shenwei.wang@nxp.com,
        xiaoning.wang@nxp.com, netdev@vger.kernel.org, linux-imx@nxp.com,
        linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH net 1/3] net: fec: dynamically set the
 NETDEV_XDP_ACT_NDO_XMIT feature of XDP
In-Reply-To: <5b1182d5-a147-4bfd-9ac8-b33462e97b10@lunn.ch>
References: <20230704082916.2135501-1-wei.fang@nxp.com>
 <20230704082916.2135501-2-wei.fang@nxp.com>
 <5b1182d5-a147-4bfd-9ac8-b33462e97b10@lunn.ch>
Date:   Wed, 05 Jul 2023 01:54:17 +0200
Message-ID: <87mt0bb5cm.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Andrew Lunn <andrew@lunn.ch> writes:

> On Tue, Jul 04, 2023 at 04:29:14PM +0800, wei.fang@nxp.com wrote:
>> From: Wei Fang <wei.fang@nxp.com>
>> 
>> When a XDP program is installed or uninstalled, fec_restart() will
>> be invoked to reset MAC and buffer descriptor rings. It's reasonable
>> not to transmit any packet during the process of reset. However, the
>> NETDEV_XDP_ACT_NDO_XMIT bit of xdp_features is enabled by default,
>> that is to say, it's possible that the fec_enet_xdp_xmit() will be
>> invoked even if the process of reset is not finished. In this case,
>> the redirected XDP frames might be dropped and available transmit BDs
>> may be incorrectly deemed insufficient. So this patch disable the
>> NETDEV_XDP_ACT_NDO_XMIT feature by default and dynamically configure
>> this feature when the bpf program is installed or uninstalled.
>
> I don't know much about XDP, so please excuse what might be a stupid
> question.
>
> Is this a generic issue? Should this
> xdp_features_clear_redirect_target(dev) /
> xdp_features_set_redirect_target(dev, false) be done in the core?

No, because not all drivers require an XDP program to be attached to
support being a redirect target (which is one of the reasons we
introduced these feature bits in the first place :)).

-Toke