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Date: Thu, 30 Apr 2026 17:57:24 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Bobby Eshleman <bobbyeshleman@gmail.com>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, Simon Horman <horms@kernel.org>, Jonathan Corbet
 <corbet@lwn.net>, Shuah Khan <skhan@linuxfoundation.org>, Alex Shi
 <alexs@kernel.org>, Yanteng Si <si.yanteng@linux.dev>, Dongliang Mu
 <dzm91@hust.edu.cn>, Michael Chan <michael.chan@broadcom.com>, Pavan Chebbi
 <pavan.chebbi@broadcom.com>, Joshua Washington <joshwash@google.com>,
 Harshitha Ramamurthy <hramamurthy@google.com>, Saeed Mahameed
 <saeedm@nvidia.com>, Tariq Toukan <tariqt@nvidia.com>, Mark Bloch
 <mbloch@nvidia.com>, Leon Romanovsky <leon@kernel.org>, Alexander Duyck
 <alexanderduyck@fb.com>, kernel-team@meta.com, Daniel Borkmann
 <daniel@iogearbox.net>, Nikolay Aleksandrov <razor@blackwall.org>, Shuah
 Khan <shuah@kernel.org>, netdev@vger.kernel.org, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
 bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Stanislav Fomichev
 <sdf@fomichev.me>, Mina Almasry <almasrymina@google.com>, Bobby Eshleman
 <bobbyeshleman@meta.com>
Subject: Re: [PATCH net-next 07/11] net: devmem: support TX over
 NETMEM_TX_NO_DMA devices
Message-ID: <20260430175724.0c134a0d@kernel.org>
In-Reply-To: <20260428-tcp-dm-netkit-v1-7-719280eba4d2@meta.com>
References: <20260428-tcp-dm-netkit-v1-0-719280eba4d2@meta.com>
	<20260428-tcp-dm-netkit-v1-7-719280eba4d2@meta.com>
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On Tue, 28 Apr 2026 15:42:04 -0700 Bobby Eshleman wrote:
>  	shinfo = skb_shinfo(skb);
> +	if (shinfo->nr_frags == 0)
> +		goto out;

Feels tempting to cover the NETMEM_TX_NO_DMA / NETMEM_TX_NONE
cases here before we even look at the frags?

> -	if (shinfo->nr_frags > 0) {
> -		niov = netmem_to_net_iov(skb_frag_netmem(&shinfo->frags[0]));
> -		if (net_is_devmem_iov(niov) &&
> -		    READ_ONCE(net_devmem_iov_binding(niov)->dev) != dev)
> +	niov = netmem_to_net_iov(skb_frag_netmem(&shinfo->frags[0]));
> +	if (!net_is_devmem_iov(niov))
> +		goto out;
> +
> +	binding = net_devmem_iov_binding(niov);
> +
> +	switch (dev->netmem_tx) {
> +	case NETMEM_TX_DMA:
> +		if (READ_ONCE(binding->dev) != dev)
>  			goto out_free;
> +		break;
> +	case NETMEM_TX_NO_DMA:
> +		break;
> +	default: /* NETMEM_TX_NONE */
> +		goto out_free;
>  	}