[RFC net-next v3 4/7] net/mlx5e: add op for getting netdev DMA device

[Dragos Tatulea <dtatulea@nvidia.com>]

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;
+out:
+	mutex_unlock(&priv->state_lock);
+
+	return pdev;
+}
+
 static const struct netdev_queue_mgmt_ops mlx5e_queue_mgmt_ops = {
 	.ndo_queue_mem_size	=	sizeof(struct mlx5_qmgmt_data),
 	.ndo_queue_mem_alloc	=	mlx5e_queue_mem_alloc,
 	.ndo_queue_mem_free	=	mlx5e_queue_mem_free,
 	.ndo_queue_start	=	mlx5e_queue_start,
 	.ndo_queue_stop		=	mlx5e_queue_stop,
+	.ndo_queue_get_dma_dev	=	mlx5e_queue_get_dma_dev,
 };
 
 static void mlx5e_build_nic_netdev(struct net_device *netdev)
-- 
2.50.1