net: devmem: allow peer-to-peer dma-buf attach for bindings

net_devmem_bind_dmabuf() uses dma_buf_attach(), a static attachment
with peer2peer false. Exporters must then keep the buffer reachable
without P2P; amdgpu does so by placing it in GTT (system memory), so a
device memory binding silently ends up in host memory.

Use dma_buf_dynamic_attach() with allow_peer2peer set, so an exporter
that can do P2P to the device keeps the buffer in device memory.
Dynamic attachments are not pinned on map, and devmem cannot handle the
buffer moving, so:

- pin it with dma_buf_pin() before mapping, which keeps it in place for
  the lifetime of the binding, as before;
- wait for the exporter's kernel fences after mapping, interruptibly,
  as the core does for static attachments.

This follows the pinned RDMA umem path, including its limits: the
binding cannot be revoked by the exporter, and once a P2P binding has
pinned a buffer in device memory, a later attachment to the same buffer
that cannot do P2P may fail to pin it. Exporters that cannot do P2P to
the device place the buffer as before. RX and TX bindings both go
through this function.

Signed-off-by: Erfan Sharafzadeh <erfansh@meta.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20261013210954.2170175-1-erfansh@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions