[PATCH net-next v3 5/5] net: Document memory provider driver support

[Mina Almasry <almasrymina@google.com>]

Document expectations from drivers looking to add support for device
memory tcp or other memory provider based features.

Signed-off-by: Mina Almasry <almasrymina@google.com>

---
 Documentation/networking/index.rst           |  1 +
 Documentation/networking/memory-provider.rst | 52 ++++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 Documentation/networking/memory-provider.rst

diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 46c178e564b3..c184e86a6ce1 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -73,6 +73,7 @@ Contents:
    l2tp
    lapb-module
    mac80211-injection
+   memory-provider
    mctp
    mpls-sysctl
    mptcp
diff --git a/Documentation/networking/memory-provider.rst b/Documentation/networking/memory-provider.rst
new file mode 100644
index 000000000000..4eee3b01eb18
--- /dev/null
+++ b/Documentation/networking/memory-provider.rst
@@ -0,0 +1,52 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================
+Memory providers
+================
+
+
+Intro
+=====
+
+Device memory TCP, and likely more upcoming features, are reliant in memory
+provider support in the driver.
+
+
+Driver support
+==============
+
+1. The driver must support page_pool. The driver must not do its own recycling
+   on top of page_pool.
+
+2. The driver must support tcp-data-split ethtool option.
+
+3. The driver must use the page_pool netmem APIs. The netmem APIs are
+   currently 1-to-1 mapped with page APIs. Conversion to netmem should be
+   achievable by switching the page APIs to netmem APIs and tracking memory via
+   netmem_refs in the driver rather than struct page * :
+
+   - page_pool_alloc -> page_pool_alloc_netmem
+   - page_pool_get_dma_addr -> page_pool_get_dma_addr_netmem
+   - page_pool_put_page -> page_pool_put_netmem
+
+   Not all page APIs have netmem equivalents at the moment. If your driver
+   relies on a missing netmem API, feel free to add and propose to netdev@ or
+   reach out to almasrymina@google.com for help adding the netmem API.
+
+4. The driver must use the following PP_FLAGS:
+
+   - PP_FLAG_DMA_MAP: netmem is not dma mappable by the driver. The driver
+     must delegate the dma mapping to the page_pool.
+   - PP_FLAG_DMA_SYNC_DEV: netmem dma addr is not necessarily dma-syncable
+     by the driver. The driver must delegate the dma syncing to the page_pool.
+   - PP_FLAG_ALLOW_UNREADABLE_NETMEM. The driver must specify this flag iff
+     tcp-data-split is enabled. In this case the netmem allocated by the
+     page_pool may be unreadable, and netmem_address() will return NULL to
+     indicate that. The driver must not assume that the netmem is readable.
+
+5. The driver must use page_pool_dma_sync_netmem_for_cpu() in lieu of
+   dma_sync_single_range_for_cpu(). For some memory providers, dma_syncing for
+   CPU will be done by the page_pool, for others (particularly dmabuf memory
+   provider), dma syncing for CPU is the responsibility of the userspace using
+   dmabuf APIs. The driver must delegate the entire dma-syncing operation to
+   the page_pool which will do it correctly.
-- 
2.47.0.338.g60cca15819-goog