Re: [RFC net-next v3 4/7] net/mlx5e: add op for getting netdev DMA device
From: Mina Almasry <hidden>
Date: 2025-08-15 17:37:29
Also in:
linux-rdma, lkml
On Fri, Aug 15, 2025 at 4:07 AM Dragos Tatulea [off-list ref] wrote:
quoted hunk ↗ jump to hunk
For zero-copy (devmem, io_uring), the netdev DMA device used is the parent device of the net device. However that is not always accurate for mlx5 devices: - SFs: The parent device is an auxdev. - Multi-PF netdevs: The DMA device should be determined by the queue. This change implements the DMA device queue API that returns the DMA device appropriately for all cases. Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com> --- .../net/ethernet/mellanox/mlx5/core/en_main.c | 24 +++++++++++++++++++ 1 file changed, 24 insertions(+)diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c index 21bb88c5d3dc..0e48065a46eb 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c@@ -5625,12 +5625,36 @@ static int mlx5e_queue_start(struct net_device *dev, void *newq, return 0; } +static struct device *mlx5e_queue_get_dma_dev(struct net_device *dev, + int queue_index) +{ + struct mlx5e_priv *priv = netdev_priv(dev); + struct mlx5e_channels *channels; + struct device *pdev = NULL; + struct mlx5e_channel *ch; + + channels = &priv->channels; + + mutex_lock(&priv->state_lock); + + if (queue_index >= channels->num) + goto out; + + ch = channels->c[queue_index]; + pdev = ch->pdev;
This code assumes priv is initialized, and probably that the device is up/running/registered. At first I thought that was fine, but now that I look at the code more closely, netdev_nl_bind_rx_doit checks if the device is present but doesn't seem to check that the device is registered. I wonder if we should have a generic check in netdev_nl_bind_rx_doit for NETDEV_REGISTERED, and if not, does this code handle unregistered netdev correctly (like netdev_priv and priv->channels are valid even for unregistered mlx5 devices)? -- Thanks, Mina