[RFC net-next v3 1/7] queue_api: add support for fetching per queue DMA dev
From: Dragos Tatulea <dtatulea@nvidia.com>
Date: 2025-08-15 11:07:05
Also in:
lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
For zerocopy (io_uring, devmem), there is an assumption that the parent device can do DMA. However that is not always the case: - Scalable Function netdevs [1] have the DMA device in the grandparent. - For Multi-PF netdevs [2] queues can be associated to different DMA devices. This patch introduces the a queue based interface for allowing drivers to expose a different DMA device for zerocopy. [1] Documentation/networking/device_drivers/ethernet/mellanox/mlx5/switchdev.rst [2] Documentation/networking/multi-pf-netdev.rst Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com> --- include/net/netdev_queues.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)
diff --git a/include/net/netdev_queues.h b/include/net/netdev_queues.h
index 6e835972abd1..d4d8c42b809f 100644
--- a/include/net/netdev_queues.h
+++ b/include/net/netdev_queues.h@@ -127,6 +127,10 @@ void netdev_stat_queue_sum(struct net_device *netdev, * @ndo_queue_stop: Stop the RX queue at the specified index. The stopped * queue's memory is written at the specified address. * + * @ndo_queue_get_dma_dev: Get dma device for zero-copy operations to be used + * for this queue. When such device is not available, + * the function will return NULL. + * * Note that @ndo_queue_mem_alloc and @ndo_queue_mem_free may be called while * the interface is closed. @ndo_queue_start and @ndo_queue_stop will only * be called for an interface which is open.
@@ -144,6 +148,8 @@ struct netdev_queue_mgmt_ops { int (*ndo_queue_stop)(struct net_device *dev, void *per_queue_mem, int idx); + struct device * (*ndo_queue_get_dma_dev)(struct net_device *dev, + int idx); }; /**
@@ -321,4 +327,18 @@ static inline void netif_subqueue_sent(const struct net_device *dev, get_desc, start_thrs); \ }) +static inline struct device * +netdev_queue_get_dma_dev(struct net_device *dev, int idx) +{ + const struct netdev_queue_mgmt_ops *queue_ops = dev->queue_mgmt_ops; + struct device *dma_dev; + + if (queue_ops && queue_ops->ndo_queue_get_dma_dev) + dma_dev = queue_ops->ndo_queue_get_dma_dev(dev, idx); + else + dma_dev = dev->dev.parent; + + return dma_dev && dma_dev->dma_mask ? dma_dev : NULL; +} + #endif
--
2.50.1