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queue_api: add support for fetching per queue DMA dev

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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>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250827144017.1529208-3-dtatulea@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Dragos Tatulea
2025-08-27 17:39:55 +03:00
committed by Jakub Kicinski
parent 14cd01c28f
commit 13d8e05adf
3 changed files with 35 additions and 0 deletions
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7
include/net/netdev_queues.h
View File

@@ -127,6 +127,9 @@ 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. Return NULL on error.
*
* 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 +147,8 @@ 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 +326,6 @@ static inline void netif_subqueue_sent(const struct net_device *dev,
get_desc, start_thrs); \
})
struct device *netdev_queue_get_dma_dev(struct net_device *dev, int idx);
#endif

1
net/core/Makefile
View File

@@ -20,6 +20,7 @@ obj-$(CONFIG_NETDEV_ADDR_LIST_TEST) += dev_addr_lists_test.o
obj-y += net-sysfs.o
obj-y += hotdata.o
obj-y += netdev_rx_queue.o
obj-y += netdev_queues.o
obj-$(CONFIG_PAGE_POOL) += page_pool.o page_pool_user.o
obj-$(CONFIG_PROC_FS) += net-procfs.o
obj-$(CONFIG_NET_PKTGEN) += pktgen.o

27
net/core/netdev_queues.c Normal file
View File

@@ -0,0 +1,27 @@
// SPDX-License-Identifier: GPL-2.0-or-later
#include <net/netdev_queues.h>
/**
* netdev_queue_get_dma_dev() - get dma device for zero-copy operations
* @dev: net_device
* @idx: queue index
*
* Get dma device for zero-copy operations to be used for this queue.
* When such device is not available or valid, the function will return NULL.
*
* Return: Device or NULL on error
*/
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;
}