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From: Benjamin Tissoires <bentiss@kernel.org>
Date: Tue, 28 May 2024 15:14:49 +0200
Subject: [PATCH HID 11/13] Documentation: HID: add a small blurb on
 udev-hid-bpf
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Message-Id: <20240528-hid_bpf_struct_ops-v1-11-8c6663df27d8@kernel.org>
References: <20240528-hid_bpf_struct_ops-v1-0-8c6663df27d8@kernel.org>
In-Reply-To: <20240528-hid_bpf_struct_ops-v1-0-8c6663df27d8@kernel.org>
To: Shuah Khan <shuah@kernel.org>, Jiri Kosina <jikos@kernel.org>, 
 Jonathan Corbet <corbet@lwn.net>, Alexei Starovoitov <ast@kernel.org>
Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, 
 bpf@vger.kernel.org, linux-input@vger.kernel.org, linux-doc@vger.kernel.org, 
 Benjamin Tissoires <bentiss@kernel.org>

This is the current decision we took: we don't provide automatic loading
of HID-BPF by the kernel directly, but rely on an external tool for it.

This tool is currently udev-hid-bpf, so let's make people aware of it.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 Documentation/hid/hid-bpf.rst | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Documentation/hid/hid-bpf.rst b/Documentation/hid/hid-bpf.rst
index bb8457bf15dd..7b151a2aef63 100644
--- a/Documentation/hid/hid-bpf.rst
+++ b/Documentation/hid/hid-bpf.rst
@@ -129,6 +129,23 @@ When a BPF program needs to emit input events, it needs to talk with the HID
 protocol, and rely on the HID kernel processing to translate the HID data into
 input events.
 
+In-tree HID-BPF programs and ``udev-hid-bpf``
+=============================================
+
+Official device fixes are shipped in the kernel tree as source in the
+``drivers/hid/bpf/progs`` directory. This allows to add selftests to them in
+``tools/testing/selftests/hid``.
+
+However, the compilation of these objects is not part of a regular kernel compilation
+given that they need an external tool to be loaded. This tool is currently
+`udev-hid-bpf <https://libevdev.pages.freedesktop.org/udev-hid-bpf/index.html>`_.
+
+For convenience, that external repository duplicates the files from here in
+``drivers/hid/bpf/progs`` into its own ``src/bpf/stable`` directory. This allows
+distributions to not have to pull the entire kernel source tree to ship and package
+those HID-BPF fixes. ``udev-hid-bpf`` also has capabilities of handling multiple
+objects files depending on the kernel the user is running.
+
 Available types of programs
 ===========================
 

-- 
2.44.0