netdev - [RFC net-next v3 3/7] net: devmem: get netdev DMA device via new API

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Message-ID: <20250815110401.2254214-5-dtatulea@nvidia.com>
Date: Fri, 15 Aug 2025 14:03:44 +0300
From: Dragos Tatulea <dtatulea@...dia.com>
To: <almasrymina@...gle.com>, <asml.silence@...il.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>
CC: Dragos Tatulea <dtatulea@...dia.com>, <cratiu@...dia.com>,
	<tariqt@...dia.com>, <parav@...dia.com>, Christoph Hellwig
	<hch@...radead.org>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [RFC net-next v3 3/7] net: devmem: get netdev DMA device via new API

Switch to the new API for fetching DMA devices for a netdev. The API is
called with queue index 0 for now which is equivalent with the previous
behavior.

This patch will allow devmem to work with devices where the DMA device
is not stored in the parent device. mlx5 SFs are an example of such a
device.

Multi-PF netdevs are still problematic (as they were before this
change). Upcoming patches will address this for the rx binding.

Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
---
 net/core/devmem.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index 24c591ab38ae..d66cb0a63bd6 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -182,6 +182,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 {
 	struct net_devmem_dmabuf_binding *binding;
 	static u32 id_alloc_next;
+	struct device *dma_dev;
 	struct scatterlist *sg;
 	struct dma_buf *dmabuf;
 	unsigned int sg_idx, i;
@@ -192,6 +193,13 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 	if (IS_ERR(dmabuf))
 		return ERR_CAST(dmabuf);
 
+	dma_dev = netdev_queue_get_dma_dev(dev, 0);
+	if (!dma_dev) {
+		err = -EOPNOTSUPP;
+		NL_SET_ERR_MSG(extack, "Device doesn't support dma");
+		goto err_put_dmabuf;
+	}
+
 	binding = kzalloc_node(sizeof(*binding), GFP_KERNEL,
 			       dev_to_node(&dev->dev));
 	if (!binding) {
@@ -209,7 +217,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 	binding->dmabuf = dmabuf;
 	binding->direction = direction;
 
-	binding->attachment = dma_buf_attach(binding->dmabuf, dev->dev.parent);
+	binding->attachment = dma_buf_attach(binding->dmabuf, dma_dev);
 	if (IS_ERR(binding->attachment)) {
 		err = PTR_ERR(binding->attachment);
 		NL_SET_ERR_MSG(extack, "Failed to bind dmabuf to device");
-- 
2.50.1