On Mon, Aug 18, 2025 at 10:40 AM Dragos Tatulea [off-list ref] wrote:

On Fri, Aug 15, 2025 at 10:37:15AM -0700, Mina Almasry wrote:

quoted

On Fri, Aug 15, 2025 at 4:07 AM Dragos Tatulea [off-list ref] wrote:

quoted

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)?

netdev_get_by_index_lock() returns non-NULL only when the device is in
state NETDEV_REGISTERED or NETREG_UNINITIALIZED. So I think  that this
check should suffice.

Ack, thanks for checking. For the patch:

Reviewed-by: Mina Almasry <redacted>



-- 
Thanks,
Mina