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Message-Id: <20240410-bpf_sources-v1-2-a8bf16033ef8@kernel.org>
Date: Wed, 10 Apr 2024 19:19:22 +0200
From: Benjamin Tissoires <bentiss@...nel.org>
To: Jiri Kosina <jikos@...nel.org>, Benjamin Tissoires <bentiss@...nel.org>,
Shuah Khan <shuah@...nel.org>, Peter Hutterer <peter.hutterer@...-t.net>
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH 02/18] HID: bpf: add first in-tree HID-BPF fix for the
XPPen Artist 24
This commit adds a fix for XPPen Artist 24 where the second button on
the pen is used as an eraser.
It's a "feature" from Microsoft, but it turns out that it's actually
painful for artists. So we ship here a HID-BPF program that turns this
second button into an actual button.
Note that the HID-BPF program is not directly loaded by the kernel itself
but by udev-hid-bpf[0]. But having the sources here allows us to also
integrate tests into tools/testing/selftests/hid to ensure the HID-BPF
program are actually tested.
[0] https://gitlab.freedesktop.org/libevdev/udev-hid-bpf
Signed-off-by: Benjamin Tissoires <bentiss@...nel.org>
---
drivers/hid/bpf/progs/Makefile | 91 +++++++++++
drivers/hid/bpf/progs/README | 102 +++++++++++++
drivers/hid/bpf/progs/XPPen__Artist24.bpf.c | 229 ++++++++++++++++++++++++++++
drivers/hid/bpf/progs/hid_bpf.h | 15 ++
drivers/hid/bpf/progs/hid_bpf_helpers.h | 170 +++++++++++++++++++++
5 files changed, 607 insertions(+)
diff --git a/drivers/hid/bpf/progs/Makefile b/drivers/hid/bpf/progs/Makefile
new file mode 100644
index 000000000000..63ed7e02adf1
--- /dev/null
+++ b/drivers/hid/bpf/progs/Makefile
@@ -0,0 +1,91 @@
+# SPDX-License-Identifier: GPL-2.0
+OUTPUT := .output
+abs_out := $(abspath $(OUTPUT))
+
+CLANG ?= clang
+LLC ?= llc
+LLVM_STRIP ?= llvm-strip
+
+TOOLS_PATH := $(abspath ../../../../tools)
+BPFTOOL_SRC := $(TOOLS_PATH)/bpf/bpftool
+BPFTOOL_OUTPUT := $(abs_out)/bpftool
+DEFAULT_BPFTOOL := $(BPFTOOL_OUTPUT)/bootstrap/bpftool
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+
+LIBBPF_SRC := $(TOOLS_PATH)/lib/bpf
+LIBBPF_OUTPUT := $(abs_out)/libbpf
+LIBBPF_DESTDIR := $(LIBBPF_OUTPUT)
+LIBBPF_INCLUDE := $(LIBBPF_DESTDIR)/include
+BPFOBJ := $(LIBBPF_OUTPUT)/libbpf.a
+
+INCLUDES := -I$(OUTPUT) -I$(LIBBPF_INCLUDE) -I$(TOOLS_PATH)/include/uapi
+CFLAGS := -g -Wall
+
+VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux) \
+ $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux) \
+ ../../../../vmlinux \
+ /sys/kernel/btf/vmlinux \
+ /boot/vmlinux-$(shell uname -r)
+VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
+ifeq ($(VMLINUX_BTF),)
+$(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
+endif
+
+ifeq ($(V),1)
+Q =
+msg =
+else
+Q = @
+msg = @printf ' %-8s %s%s\n' "$(1)" "$(notdir $(2))" "$(if $(3), $(3))";
+MAKEFLAGS += --no-print-directory
+submake_extras := feature_display=0
+endif
+
+.DELETE_ON_ERROR:
+
+.PHONY: all clean
+
+SOURCES = $(wildcard *.bpf.c)
+TARGETS = $(SOURCES:.bpf.c=.bpf.o)
+
+all: $(TARGETS)
+
+clean:
+ $(call msg,CLEAN)
+ $(Q)rm -rf $(OUTPUT) $(TARGETS)
+
+%.bpf.o: %.bpf.c vmlinux.h $(BPFOBJ) | $(OUTPUT)
+ $(call msg,BPF,$@)
+ $(Q)$(CLANG) -g -O2 --target=bpf $(INCLUDES) \
+ -c $(filter %.c,$^) -o $@ && \
+ $(LLVM_STRIP) -g $@
+
+vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR)
+ifeq ($(VMLINUX_H),)
+ $(call msg,GEN,,$@)
+ $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@
+else
+ $(call msg,CP,,$@)
+ $(Q)cp "$(VMLINUX_H)" $@
+endif
+
+$(OUTPUT) $(LIBBPF_OUTPUT) $(BPFTOOL_OUTPUT):
+ $(call msg,MKDIR,$@)
+ $(Q)mkdir -p $@
+
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUTPUT)
+ $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) \
+ OUTPUT=$(abspath $(dir $@))/ prefix= \
+ DESTDIR=$(LIBBPF_DESTDIR) $(abspath $@) install_headers
+
+ifeq ($(CROSS_COMPILE),)
+$(DEFAULT_BPFTOOL): $(BPFOBJ) | $(BPFTOOL_OUTPUT)
+ $(Q)$(MAKE) $(submake_extras) -C $(BPFTOOL_SRC) \
+ OUTPUT=$(BPFTOOL_OUTPUT)/ \
+ LIBBPF_BOOTSTRAP_OUTPUT=$(LIBBPF_OUTPUT)/ \
+ LIBBPF_BOOTSTRAP_DESTDIR=$(LIBBPF_DESTDIR)/ bootstrap
+else
+$(DEFAULT_BPFTOOL): | $(BPFTOOL_OUTPUT)
+ $(Q)$(MAKE) $(submake_extras) -C $(BPFTOOL_SRC) \
+ OUTPUT=$(BPFTOOL_OUTPUT)/ bootstrap
+endif
diff --git a/drivers/hid/bpf/progs/README b/drivers/hid/bpf/progs/README
new file mode 100644
index 000000000000..20b0928f385b
--- /dev/null
+++ b/drivers/hid/bpf/progs/README
@@ -0,0 +1,102 @@
+# HID-BPF programs
+
+This directory contains various fixes for devices. They add new features or
+fix some behaviors without being entirely mandatory. It is better to load them
+when you have such a device, but they should not be a requirement for a device
+to be working during the boot stage.
+
+The .bpf.c files provided here are not automatically compiled in the kernel.
+They should be loaded in the kernel by `udev-hid-bpf`:
+
+https://gitlab.freedesktop.org/libevdev/udev-hid-bpf
+
+The main reasons for these fixes to be here is to have a central place to
+"upstream" them, but also this way we can test them thanks to the HID
+selftests.
+
+Once a .bpf.c file is accepted here, it is duplicated in `udev-hid-bpf`
+in the `src/bpf/stable` directory, and distributions are encouraged to
+only ship those bpf objects. So adding a file here should eventually
+land in distributions when they update `udev-hid-bpf`
+
+## Compilation
+
+Just run `make`
+
+## Installation
+
+### Automated way
+
+Just run `sudo udev-hid-bpf install ./my-awesome-fix.bpf.o`
+
+### Manual way
+
+- copy the `.bpf.o` you want in `/etc/udev-hid-bpf/`
+- create a new udev rule to automatically load it
+
+The following should do the trick (assuming udev-hid-bpf is available in
+/usr/bin):
+
+```
+$> cp xppen-ArtistPro16Gen2.bpf.o /etc/udev-hid-bpf/
+$> udev-hid-bpf inspect xppen-ArtistPro16Gen2.bpf.o
+[
+ {
+ "name": "xppen-ArtistPro16Gen2.bpf.o",
+ "devices": [
+ {
+ "bus": "0x0003",
+ "group": "0x0001",
+ "vid": "0x28BD",
+ "pid": "0x095A"
+ },
+ {
+ "bus": "0x0003",
+ "group": "0x0001",
+ "vid": "0x28BD",
+ "pid": "0x095B"
+ }
+ ],
+...
+$> cat <EOF > /etc/udev/rules.d/99-load-hid-bpf-xppen-ArtistPro16Gen2.rules
+ACTION!="add|remove", GOTO="hid_bpf_end"
+SUBSYSTEM!="hid", GOTO="hid_bpf_end"
+
+# xppen-ArtistPro16Gen2.bpf.o
+ACTION=="add",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095A", RUN{program}+="/usr/local/bin/udev-hid-bpf add $sys$devpath /etc/udev-hid-bpf/xppen-ArtistPro16Gen2.bpf.o"
+ACTION=="remove",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095A", RUN{program}+="/usr/local/bin/udev-hid-bpf remove $sys$devpath "
+# xppen-ArtistPro16Gen2.bpf.o
+ACTION=="add",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095B", RUN{program}+="/usr/local/bin/udev-hid-bpf add $sys$devpath /etc/udev-hid-bpf/xppen-ArtistPro16Gen2.bpf.o"
+ACTION=="remove",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095B", RUN{program}+="/usr/local/bin/udev-hid-bpf remove $sys$devpath "
+
+LABEL="hid_bpf_end"
+EOF
+$> udevadm control --reload
+```
+
+Then unplug and replug the device.
+
+## Checks
+
+### udev rule
+
+You can check that the udev rule is correctly working by issuing
+
+```
+$> udevadm test /sys/bus/hid/devices/0003:28BD:095B*
+...
+run: '/usr/local/bin/udev-hid-bpf add /sys/devices/virtual/misc/uhid/0003:28BD:095B.0E57 /etc/udev-hid-bpf/xppen-ArtistPro16Gen2.bpf.o'
+```
+
+### program loaded
+
+You can check that the program has been properly loaded with `bpftool`
+
+```
+$> bpftool prog
+...
+247: tracing name xppen_16_fix_eraser tag 18d389353ed2ef07 gpl
+ loaded_at 2024-03-28T16:02:28+0100 uid 0
+ xlated 120B jited 77B memlock 4096B
+ btf_id 487
+```
diff --git a/drivers/hid/bpf/progs/XPPen__Artist24.bpf.c b/drivers/hid/bpf/progs/XPPen__Artist24.bpf.c
new file mode 100644
index 000000000000..e1be6a12bb75
--- /dev/null
+++ b/drivers/hid/bpf/progs/XPPen__Artist24.bpf.c
@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2023 Benjamin Tissoires
+ */
+
+#include "vmlinux.h"
+#include "hid_bpf.h"
+#include "hid_bpf_helpers.h"
+#include <bpf/bpf_tracing.h>
+
+#define VID_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */
+#define PID_ARTIST_24 0x093A
+#define PID_ARTIST_24_PRO 0x092D
+
+HID_BPF_CONFIG(
+ HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24),
+ HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24_PRO)
+);
+
+/*
+ * We need to amend the report descriptor for the following:
+ * - the device reports Eraser instead of using Secondary Barrel Switch
+ * - the pen doesn't have a rubber tail, so basically we are removing any
+ * eraser/invert bits
+ */
+static const __u8 fixed_rdesc[] = {
+ 0x05, 0x0d, // Usage Page (Digitizers) 0
+ 0x09, 0x02, // Usage (Pen) 2
+ 0xa1, 0x01, // Collection (Application) 4
+ 0x85, 0x07, // Report ID (7) 6
+ 0x09, 0x20, // Usage (Stylus) 8
+ 0xa1, 0x00, // Collection (Physical) 10
+ 0x09, 0x42, // Usage (Tip Switch) 12
+ 0x09, 0x44, // Usage (Barrel Switch) 14
+ 0x09, 0x5a, // Usage (Secondary Barrel Switch) 16 /* changed from 0x45 (Eraser) to 0x5a (Secondary Barrel Switch) */
+ 0x15, 0x00, // Logical Minimum (0) 18
+ 0x25, 0x01, // Logical Maximum (1) 20
+ 0x75, 0x01, // Report Size (1) 22
+ 0x95, 0x03, // Report Count (3) 24
+ 0x81, 0x02, // Input (Data,Var,Abs) 26
+ 0x95, 0x02, // Report Count (2) 28
+ 0x81, 0x03, // Input (Cnst,Var,Abs) 30
+ 0x09, 0x32, // Usage (In Range) 32
+ 0x95, 0x01, // Report Count (1) 34
+ 0x81, 0x02, // Input (Data,Var,Abs) 36
+ 0x95, 0x02, // Report Count (2) 38
+ 0x81, 0x03, // Input (Cnst,Var,Abs) 40
+ 0x75, 0x10, // Report Size (16) 42
+ 0x95, 0x01, // Report Count (1) 44
+ 0x35, 0x00, // Physical Minimum (0) 46
+ 0xa4, // Push 48
+ 0x05, 0x01, // Usage Page (Generic Desktop) 49
+ 0x09, 0x30, // Usage (X) 51
+ 0x65, 0x13, // Unit (EnglishLinear: in) 53
+ 0x55, 0x0d, // Unit Exponent (-3) 55
+ 0x46, 0xf0, 0x50, // Physical Maximum (20720) 57
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 60
+ 0x81, 0x02, // Input (Data,Var,Abs) 63
+ 0x09, 0x31, // Usage (Y) 65
+ 0x46, 0x91, 0x2d, // Physical Maximum (11665) 67
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 70
+ 0x81, 0x02, // Input (Data,Var,Abs) 73
+ 0xb4, // Pop 75
+ 0x09, 0x30, // Usage (Tip Pressure) 76
+ 0x45, 0x00, // Physical Maximum (0) 78
+ 0x26, 0xff, 0x1f, // Logical Maximum (8191) 80
+ 0x81, 0x42, // Input (Data,Var,Abs,Null) 83
+ 0x09, 0x3d, // Usage (X Tilt) 85
+ 0x15, 0x81, // Logical Minimum (-127) 87
+ 0x25, 0x7f, // Logical Maximum (127) 89
+ 0x75, 0x08, // Report Size (8) 91
+ 0x95, 0x01, // Report Count (1) 93
+ 0x81, 0x02, // Input (Data,Var,Abs) 95
+ 0x09, 0x3e, // Usage (Y Tilt) 97
+ 0x15, 0x81, // Logical Minimum (-127) 99
+ 0x25, 0x7f, // Logical Maximum (127) 101
+ 0x81, 0x02, // Input (Data,Var,Abs) 103
+ 0xc0, // End Collection 105
+ 0xc0, // End Collection 106
+};
+
+#define BIT(n) (1UL << n)
+
+#define TIP_SWITCH BIT(0)
+#define BARREL_SWITCH BIT(1)
+#define ERASER BIT(2)
+/* padding BIT(3) */
+/* padding BIT(4) */
+#define IN_RANGE BIT(5)
+/* padding BIT(6) */
+/* padding BIT(7) */
+
+#define U16(index) (data[index] | (data[index + 1] << 8))
+
+SEC("fmod_ret/hid_bpf_rdesc_fixup")
+int BPF_PROG(hid_fix_rdesc_xppen_artist24, struct hid_bpf_ctx *hctx)
+{
+ __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);
+
+ if (!data)
+ return 0; /* EPERM check */
+
+ __builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc));
+
+ return sizeof(fixed_rdesc);
+}
+
+static __u8 prev_state = 0;
+
+/*
+ * There are a few cases where the device is sending wrong event
+ * sequences, all related to the second button (the pen doesn't
+ * have an eraser switch on the tail end):
+ *
+ * whenever the second button gets pressed or released, an
+ * out-of-proximity event is generated and then the firmware
+ * compensate for the missing state (and the firmware uses
+ * eraser for that button):
+ *
+ * - if the pen is in range, an extra out-of-range is sent
+ * when the second button is pressed/released:
+ * // Pen is in range
+ * E: InRange
+ *
+ * // Second button is pressed
+ * E:
+ * E: Eraser InRange
+ *
+ * // Second button is released
+ * E:
+ * E: InRange
+ *
+ * This case is ignored by this filter, it's "valid"
+ * and userspace knows how to deal with it, there are just
+ * a few out-of-prox events generated, but the user doesn´t
+ * see them.
+ *
+ * - if the pen is in contact, 2 extra events are added when
+ * the second button is pressed/released: an out of range
+ * and an in range:
+ *
+ * // Pen is in contact
+ * E: TipSwitch InRange
+ *
+ * // Second button is pressed
+ * E: <- false release, needs to be filtered out
+ * E: Eraser InRange <- false release, needs to be filtered out
+ * E: TipSwitch Eraser InRange
+ *
+ * // Second button is released
+ * E: <- false release, needs to be filtered out
+ * E: InRange <- false release, needs to be filtered out
+ * E: TipSwitch InRange
+ *
+ */
+SEC("fmod_ret/hid_bpf_device_event")
+int BPF_PROG(xppen_24_fix_eraser, struct hid_bpf_ctx *hctx)
+{
+ __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */);
+ __u8 current_state, changed_state;
+ bool prev_tip;
+ __u16 tilt;
+
+ if (!data)
+ return 0; /* EPERM check */
+
+ current_state = data[1];
+
+ /* if the state is identical to previously, early return */
+ if (current_state == prev_state)
+ return 0;
+
+ prev_tip = !!(prev_state & TIP_SWITCH);
+
+ /*
+ * Illegal transition: pen is in range with the tip pressed, and
+ * it goes into out of proximity.
+ *
+ * Ideally we should hold the event, start a timer and deliver it
+ * only if the timer ends, but we are not capable of that now.
+ *
+ * And it doesn't matter because when we are in such cases, this
+ * means we are detecting a false release.
+ */
+ if ((current_state & IN_RANGE) == 0) {
+ if (prev_tip)
+ return HID_IGNORE_EVENT;
+ return 0;
+ }
+
+ /*
+ * XOR to only set the bits that have changed between
+ * previous and current state
+ */
+ changed_state = prev_state ^ current_state;
+
+ /* Store the new state for future processing */
+ prev_state = current_state;
+
+ /*
+ * We get both a tipswitch and eraser change in the same HID report:
+ * this is not an authorized transition and is unlikely to happen
+ * in real life.
+ * This is likely to be added by the firmware to emulate the
+ * eraser mode so we can skip the event.
+ */
+ if ((changed_state & (TIP_SWITCH | ERASER)) == (TIP_SWITCH | ERASER)) /* we get both a tipswitch and eraser change at the same time */
+ return HID_IGNORE_EVENT;
+
+ return 0;
+}
+
+SEC("syscall")
+int probe(struct hid_bpf_probe_args *ctx)
+{
+ /*
+ * The device exports 3 interfaces.
+ */
+ ctx->retval = ctx->rdesc_size != 107;
+ if (ctx->retval)
+ ctx->retval = -EINVAL;
+
+ /* ensure the kernel isn't fixed already */
+ if (ctx->rdesc[17] != 0x45) /* Eraser */
+ ctx->retval = -EINVAL;
+
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/drivers/hid/bpf/progs/hid_bpf.h b/drivers/hid/bpf/progs/hid_bpf.h
new file mode 100644
index 000000000000..7ee371cac2e1
--- /dev/null
+++ b/drivers/hid/bpf/progs/hid_bpf.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2022 Benjamin Tissoires
+ */
+
+#ifndef ____HID_BPF__H
+#define ____HID_BPF__H
+
+struct hid_bpf_probe_args {
+ unsigned int hid;
+ unsigned int rdesc_size;
+ unsigned char rdesc[4096];
+ int retval;
+};
+
+#endif /* ____HID_BPF__H */
diff --git a/drivers/hid/bpf/progs/hid_bpf_helpers.h b/drivers/hid/bpf/progs/hid_bpf_helpers.h
new file mode 100644
index 000000000000..1d53b10aaa2e
--- /dev/null
+++ b/drivers/hid/bpf/progs/hid_bpf_helpers.h
@@ -0,0 +1,170 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2022 Benjamin Tissoires
+ */
+
+#ifndef __HID_BPF_HELPERS_H
+#define __HID_BPF_HELPERS_H
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <linux/errno.h>
+
+extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx,
+ unsigned int offset,
+ const size_t __sz) __ksym;
+extern struct hid_bpf_ctx *hid_bpf_allocate_context(unsigned int hid_id) __ksym;
+extern void hid_bpf_release_context(struct hid_bpf_ctx *ctx) __ksym;
+extern int hid_bpf_hw_request(struct hid_bpf_ctx *ctx,
+ __u8 *data,
+ size_t buf__sz,
+ enum hid_report_type type,
+ enum hid_class_request reqtype) __ksym;
+
+#define HID_MAX_DESCRIPTOR_SIZE 4096
+#define HID_IGNORE_EVENT -1
+
+/* extracted from <linux/input.h> */
+#define BUS_ANY 0x00
+#define BUS_PCI 0x01
+#define BUS_ISAPNP 0x02
+#define BUS_USB 0x03
+#define BUS_HIL 0x04
+#define BUS_BLUETOOTH 0x05
+#define BUS_VIRTUAL 0x06
+#define BUS_ISA 0x10
+#define BUS_I8042 0x11
+#define BUS_XTKBD 0x12
+#define BUS_RS232 0x13
+#define BUS_GAMEPORT 0x14
+#define BUS_PARPORT 0x15
+#define BUS_AMIGA 0x16
+#define BUS_ADB 0x17
+#define BUS_I2C 0x18
+#define BUS_HOST 0x19
+#define BUS_GSC 0x1A
+#define BUS_ATARI 0x1B
+#define BUS_SPI 0x1C
+#define BUS_RMI 0x1D
+#define BUS_CEC 0x1E
+#define BUS_INTEL_ISHTP 0x1F
+#define BUS_AMD_SFH 0x20
+
+/* extracted from <linux/hid.h> */
+#define HID_GROUP_ANY 0x0000
+#define HID_GROUP_GENERIC 0x0001
+#define HID_GROUP_MULTITOUCH 0x0002
+#define HID_GROUP_SENSOR_HUB 0x0003
+#define HID_GROUP_MULTITOUCH_WIN_8 0x0004
+#define HID_GROUP_RMI 0x0100
+#define HID_GROUP_WACOM 0x0101
+#define HID_GROUP_LOGITECH_DJ_DEVICE 0x0102
+#define HID_GROUP_STEAM 0x0103
+#define HID_GROUP_LOGITECH_27MHZ_DEVICE 0x0104
+#define HID_GROUP_VIVALDI 0x0105
+
+/* include/linux/mod_devicetable.h defines as (~0), but that gives us negative size arrays */
+#define HID_VID_ANY 0x0000
+#define HID_PID_ANY 0x0000
+
+/* duplicated from incluse/linux/array_size.h
+ */
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+/* Helper macro to convert (foo, __LINE__) into foo134 so we can use __LINE__ for
+ * field/variable names
+ */
+#define COMBINE1(X, Y) X ## Y
+#define COMBINE(X, Y) COMBINE1(X, Y)
+
+/* Macro magic:
+ * __uint(foo, 123) creates a int (*foo)[1234]
+ *
+ * We use that macro to declare an anonymous struct with several
+ * fields, each is the declaration of an pointer to an array of size
+ * bus/group/vid/pid. (Because it's a pointer to such an array, actual storage
+ * would be sizeof(pointer) rather than sizeof(array). Not that we ever
+ * instantiate it anyway).
+ *
+ * This is only used for BTF introspection, we can later check "what size
+ * is the bus array" in the introspection data and thus extract the bus ID
+ * again.
+ *
+ * And we use the __LINE__ to give each of our structs a unique name so the
+ * BPF program writer doesn't have to.
+ *
+ * $ bpftool btf dump file target/bpf/HP_Elite_Presenter.bpf.o
+ * shows the inspection data, start by searching for .hid_bpf_config
+ * and working backwards from that (each entry references the type_id of the
+ * content).
+ */
+
+#define HID_DEVICE(b, g, ven, prod) \
+ struct { \
+ __uint(name, 0); \
+ __uint(bus, (b)); \
+ __uint(group, (g)); \
+ __uint(vid, (ven)); \
+ __uint(pid, (prod)); \
+ } COMBINE(_entry, __LINE__)
+
+/* Macro magic below is to make HID_BPF_CONFIG() look like a function call that
+ * we can pass multiple HID_DEVICE() invocations in.
+ *
+ * For up to 16 arguments, HID_BPF_CONFIG(one, two) resolves to
+ *
+ * union {
+ * HID_DEVICE(...);
+ * HID_DEVICE(...);
+ * } _device_ids SEC(".hid_bpf_config")
+ *
+ */
+
+/* Returns the number of macro arguments, this expands
+ * NARGS(a, b, c) to NTH_ARG(a, b, c, 15, 14, 13, .... 4, 3, 2, 1).
+ * NTH_ARG always returns the 16th argument which in our case is 3.
+ *
+ * If we want more than 16 values _COUNTDOWN and _NTH_ARG both need to be
+ * updated.
+ */
+#define _NARGS(...) _NARGS1(__VA_ARGS__, _COUNTDOWN)
+#define _NARGS1(...) _NTH_ARG(__VA_ARGS__)
+
+/* Add to this if we need more than 16 args */
+#define _COUNTDOWN \
+ 15, 14, 13, 12, 11, 10, 9, 8, \
+ 7, 6, 5, 4, 3, 2, 1, 0
+
+/* Return the 16 argument passed in. See _NARGS above for usage. Note this is
+ * 1-indexed.
+ */
+#define _NTH_ARG( \
+ _1, _2, _3, _4, _5, _6, _7, _8, \
+ _9, _10, _11, _12, _13, _14, _15,\
+ N, ...) N
+
+/* Turns EXPAND(_ARG, a, b, c) into _ARG3(a, b, c) */
+#define _EXPAND(func, ...) COMBINE(func, _NARGS(__VA_ARGS__)) (__VA_ARGS__)
+
+/* And now define all the ARG macros for each number of args we want to accept */
+#define _ARG1(_1) _1;
+#define _ARG2(_1, _2) _1; _2;
+#define _ARG3(_1, _2, _3) _1; _2; _3;
+#define _ARG4(_1, _2, _3, _4) _1; _2; _3; _4;
+#define _ARG5(_1, _2, _3, _4, _5) _1; _2; _3; _4; _5;
+#define _ARG6(_1, _2, _3, _4, _5, _6) _1; _2; _3; _4; _5; _6;
+#define _ARG7(_1, _2, _3, _4, _5, _6, _7) _1; _2; _3; _4; _5; _6; _7;
+#define _ARG8(_1, _2, _3, _4, _5, _6, _7, _8) _1; _2; _3; _4; _5; _6; _7; _8;
+#define _ARG9(_1, _2, _3, _4, _5, _6, _7, _8, _9) _1; _2; _3; _4; _5; _6; _7; _8; _9;
+#define _ARG10(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a;
+#define _ARG11(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b;
+#define _ARG12(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c;
+#define _ARG13(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, _d) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; _d;
+#define _ARG14(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, _d, _e) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; _d; _e;
+#define _ARG15(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, _d, _e, _f) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; _d; _e; _f;
+
+
+#define HID_BPF_CONFIG(...) union { \
+ _EXPAND(_ARG, __VA_ARGS__) \
+} _device_ids SEC(".hid_bpf_config")
+
+#endif /* __HID_BPF_HELPERS_H */
--
2.44.0
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