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([2620:10d:c092:600::1:4dfd]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ae3f66d93c8sm884341566b.11.2025.07.08.04.05.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Jul 2025 04:05:01 -0700 (PDT) Message-ID: <32cb77d8-a4a5-4fc7-a427-d723e60efc59@gmail.com> Date: Tue, 8 Jul 2025 12:06:29 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC net-next 1/4] net: Allow non parent devices to be used for ZC DMA To: Dragos Tatulea , almasrymina@google.com, Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: Saeed Mahameed , tariqt@nvidia.com, cratiu@nvidia.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250702172433.1738947-1-dtatulea@nvidia.com> <20250702172433.1738947-2-dtatulea@nvidia.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20250702172433.1738947-2-dtatulea@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/2/25 18:24, Dragos Tatulea wrote: > For zerocopy (io_uring, devmem), there is an assumption that the > parent device can do DMA. However that is not always the case: > for example mlx5 SF devices have an auxiliary device as a parent. > > This patch introduces the possibility for the driver to specify > another DMA device to be used via the new dma_dev field. The field > should be set before register_netdev(). > > A new helper function is added to get the DMA device or return NULL. > The callers can check for NULL and fail early if the device is > not capable of DMA. > > Signed-off-by: Dragos Tatulea > --- > include/linux/netdevice.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > index 5847c20994d3..83faa2314c30 100644 > --- a/include/linux/netdevice.h > +++ b/include/linux/netdevice.h > @@ -2550,6 +2550,9 @@ struct net_device { > > struct hwtstamp_provider __rcu *hwprov; > > + /* To be set by devices that can do DMA but not via parent. */ > + struct device *dma_dev; > + > u8 priv[] ____cacheline_aligned > __counted_by(priv_len); > } ____cacheline_aligned; > @@ -5560,4 +5563,14 @@ extern struct net_device *blackhole_netdev; > atomic_long_add((VAL), &(DEV)->stats.__##FIELD) > #define DEV_STATS_READ(DEV, FIELD) atomic_long_read(&(DEV)->stats.__##FIELD) > > +static inline struct device *netdev_get_dma_dev(const struct net_device *dev) > +{ > + struct device *dma_dev = dev->dma_dev ? dev->dma_dev : dev->dev.parent; > + > + if (!dma_dev->dma_mask) dev->dev.parent is NULL for veth and I assume other virtual devices as well. Mina, can you verify that devmem checks that? Seems like veth is rejected by netdev_need_ops_lock() in netdev_nl_bind_rx_doit(), but IIRC per netdev locking came after devmem got merged, and there are other virt devices that might already be converted. > + dma_dev = NULL; > + > + return dma_dev; > +} > + > #endif /* _LINUX_NETDEVICE_H */ -- Pavel Begunkov