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Date: Wed, 6 May 2026 19:30:25 -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 v2 1/6] net: add netmem_tx modes that indicate
 dma capability
Message-ID: <20260506193025.78aba2dc@kernel.org>
In-Reply-To: <20260504-tcp-dm-netkit-v2-1-56d52ac72fd4@meta.com>
References: <20260504-tcp-dm-netkit-v2-0-56d52ac72fd4@meta.com>
	<20260504-tcp-dm-netkit-v2-1-56d52ac72fd4@meta.com>
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On Mon, 04 May 2026 17:27:48 -0700 Bobby Eshleman wrote:
> --- a/drivers/net/netkit.c
> +++ b/drivers/net/netkit.c
> @@ -466,6 +466,7 @@ static void netkit_setup(struct net_device *dev)
>  	dev->priv_flags |= IFF_NO_QUEUE;
>  	dev->priv_flags |= IFF_DISABLE_NETPOLL;
>  	dev->lltx = true;
> +	dev->netmem_tx = NETMEM_TX_NO_DMA;
>  
>  	dev->netdev_ops     = &netkit_netdev_ops;
>  	dev->ethtool_ops    = &netkit_ethtool_ops;
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 0e1e581efc5a..11d68e75eb4f 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1788,6 +1788,12 @@ enum netdev_stat_type {
>  	NETDEV_PCPU_STAT_DSTATS, /* struct pcpu_dstats */
>  };
>  
> +enum netmem_tx_mode {
> +	NETMEM_TX_NONE,		/* no netmem TX support */
> +	NETMEM_TX_DMA,		/* DMA-capable netmem TX (real HW) */
> +	NETMEM_TX_NO_DMA,	/* no DMA, e.g. passthrough for virtual devs */

Now there's a little too much here, let's move the NO_DMA changes to
another patch. Just convert the netmem_tx to an enum and change the
existing drivers in patch 1.

Next patch has:

> @@ -1164,16 +1197,30 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>  		goto err_unlock_netdev;
>  	}
>  
> -	if (!netdev->netmem_tx) {
> +	if (netdev->netmem_tx == NETMEM_TX_NONE) {
>  		err = -EOPNOTSUPP;
>  		NL_SET_ERR_MSG(info->extack,
>  			       "Driver does not support netmem TX");
>  		goto err_unlock_netdev;
>  	}

which also should have been in patch 1.