Currently the kernel is scheduled to do this call by itself, but it
requires a kernel v6.18 at least to have the INPUT_PROP set. For older
kernels, we can try to query the property from a HID-BPF probe, and set
a udev property based on that. This way we can provide the information
to old kernels without modifying them.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/220
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 drivers/hid/bpf/progs/Generic__touchpad.bpf.c | 90 +++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/drivers/hid/bpf/progs/Generic__touchpad.bpf.c b/drivers/hid/bpf/progs/Generic__touchpad.bpf.c
new file mode 100644
index 000000000000..b9f2cac91724
--- /dev/null
+++ b/drivers/hid/bpf/progs/Generic__touchpad.bpf.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2025 Benjamin Tissoires
+ */
+
+#include "vmlinux.h"
+#include "hid_bpf.h"
+#include "hid_bpf_helpers.h"
+#include "hid_report_helpers.h"
+#include "hid_usages.h"
+#include <bpf/bpf_tracing.h>
+
+HID_BPF_CONFIG(
+	HID_DEVICE(BUS_ANY, HID_GROUP_MULTITOUCH_WIN_8, HID_VID_ANY, HID_PID_ANY),
+);
+
+EXPORT_UDEV_PROP(HID_DIGITIZER_PAD_TYPE, 32);
+
+__u8 hw_req_buf[1024];
+
+/* to be filled by udev-hid-bpf */
+struct hid_rdesc_descriptor HID_REPORT_DESCRIPTOR;
+
+SEC("syscall")
+int probe(struct hid_bpf_probe_args *ctx)
+{
+	struct hid_rdesc_report *pad_type_feature = NULL;
+	struct hid_rdesc_field *pad_type = NULL;
+	struct hid_rdesc_report *feature;
+	struct hid_bpf_ctx *hid_ctx;
+	char *pad_type_str = "";
+	int ret;
+
+	hid_bpf_for_each_feature_report(&HID_REPORT_DESCRIPTOR, feature) {
+		struct hid_rdesc_field *field;
+
+		hid_bpf_for_each_field(feature, field) {
+			if (field->usage_page == HidUsagePage_Digitizers &&
+			    field->usage_id == HidUsage_Dig_PadType) {
+				pad_type = field;
+				pad_type_feature = feature;
+				break;
+			}
+		}
+		if (pad_type)
+			break;
+	}
+
+	if (!pad_type || !pad_type_feature) {
+		ctx->retval = -EINVAL;
+		return 0;
+	}
+
+	hid_ctx = hid_bpf_allocate_context(ctx->hid);
+
+	if (!hid_ctx)
+		return -1; /* EPERM check */
+
+	hw_req_buf[0] = pad_type_feature->report_id;
+
+	ret = hid_bpf_hw_request(hid_ctx, hw_req_buf, sizeof(hw_req_buf),
+					HID_FEATURE_REPORT, HID_REQ_GET_REPORT);
+	hid_bpf_release_context(hid_ctx);
+
+	if (ret < 0) {
+		ctx->retval = ret;
+		return 0;
+	}
+
+	ctx->retval = 0;
+
+	switch (EXTRACT_BITS(hw_req_buf, pad_type)) {
+	case 0:
+		pad_type_str = "Clickpad";
+		break;
+	case 1:
+		pad_type_str = "Pressurepad";
+		break;
+	case 2:
+		pad_type_str = "Discrete";
+		break;
+	default:
+		pad_type_str = "Unknown";
+	}
+
+	UDEV_PROP_SPRINTF(HID_DIGITIZER_PAD_TYPE, "%s", pad_type_str);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

-- 
2.53.0