[PATCH 2/7] HID: bpf: Suppress bogus F13 trigger on Sirius keyboard full fan shortcut

[Benjamin Tissoires <bentiss@kernel.org>]

The TUXEDO Sirius 16 Gen1 and the TUXEDO Sirius 16 Gen2 Notebooks have an
additional "fan" key next to F12.

Pressing it alone sends a F14 key press which can be bound by user space.

Pressing it while holding the FN key triggers two things:
- The EC firmware locks the fan speed of the internal fans at 100%
- F13 key press is registered which by default is already bound in xkb and
  desktop environments (e.g. in KDE Plasma it launches system settings)

To avoid this unexpected double duty of the FN shortcut, this bpf program
suppresses the F13 key press.

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/166
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 .../progs/TUXEDO__Sirius-16-Gen1-and-Gen2.bpf.c    | 47 ++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/drivers/hid/bpf/progs/TUXEDO__Sirius-16-Gen1-and-Gen2.bpf.c b/drivers/hid/bpf/progs/TUXEDO__Sirius-16-Gen1-and-Gen2.bpf.c
new file mode 100644
index 0000000000000000000000000000000000000000..a123003fb5fdd0a27bc204b9b393da52b0956cfa
--- /dev/null
+++ b/drivers/hid/bpf/progs/TUXEDO__Sirius-16-Gen1-and-Gen2.bpf.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Copyright (c) 2025 TUXEDO Computers GmbH
+ */
+
+#include "vmlinux.h"
+#include "hid_bpf.h"
+#include "hid_bpf_helpers.h"
+#include <bpf/bpf_tracing.h>
+
+HID_BPF_CONFIG(
+	HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, 0x048D, 0x8910)
+);
+
+SEC(HID_BPF_DEVICE_EVENT)
+int BPF_PROG(ignore_key_fix_event, struct hid_bpf_ctx *hid_ctx)
+{
+	const int expected_length = 37;
+	const int expected_report_id = 1;
+	__u8 *data;
+	int i;
+
+	if (hid_ctx->size < expected_length)
+		return 0;
+
+	data = hid_bpf_get_data(hid_ctx, 0, expected_length);
+	if (!data || data[0] != expected_report_id)
+		return 0;
+
+	// Zero out F13 (HID usage ID: 0x68) key press.
+	// The first 6 parallel key presses (excluding modifier keys) are
+	// encoded in an array containing usage IDs.
+	for (i = 3; i < 9; ++i)
+		if (data[i] == 0x68)
+			data[i] = 0x00;
+	// Additional parallel key presses starting with the 7th (excluding
+	// modifier keys) are encoded as a bit flag with the offset being
+	// the usage ID.
+	data[22] &= 0xfe;
+
+	return 0;
+}
+
+HID_BPF_OPS(ignore_button) = {
+	.hid_device_event = (void *)ignore_key_fix_event,
+};
+
+char _license[] SEC("license") = "GPL";

-- 
2.47.0