231 lines
9 KiB
C
231 lines
9 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2023 Benjamin Tissoires
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*/
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#include "vmlinux.h"
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#include "hid_bpf.h"
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#include "hid_bpf_helpers.h"
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#include <bpf/bpf_tracing.h>
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#define VID_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */
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#define PID_ARTIST_24 0x093A
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#define PID_ARTIST_24_PRO 0x092D
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HID_BPF_CONFIG(
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HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24),
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HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24_PRO)
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);
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/*
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* We need to amend the report descriptor for the following:
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* - the device reports Eraser instead of using Secondary Barrel Switch
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* - the pen doesn't have a rubber tail, so basically we are removing any
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* eraser/invert bits
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*/
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static const __u8 fixed_rdesc[] = {
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0x05, 0x0d, // Usage Page (Digitizers) 0
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0x09, 0x02, // Usage (Pen) 2
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0xa1, 0x01, // Collection (Application) 4
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0x85, 0x07, // Report ID (7) 6
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0x09, 0x20, // Usage (Stylus) 8
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0xa1, 0x00, // Collection (Physical) 10
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0x09, 0x42, // Usage (Tip Switch) 12
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0x09, 0x44, // Usage (Barrel Switch) 14
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0x09, 0x5a, // Usage (Secondary Barrel Switch) 16 /* changed from 0x45 (Eraser) to 0x5a (Secondary Barrel Switch) */
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0x15, 0x00, // Logical Minimum (0) 18
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0x25, 0x01, // Logical Maximum (1) 20
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0x75, 0x01, // Report Size (1) 22
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0x95, 0x03, // Report Count (3) 24
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0x81, 0x02, // Input (Data,Var,Abs) 26
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0x95, 0x02, // Report Count (2) 28
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0x81, 0x03, // Input (Cnst,Var,Abs) 30
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0x09, 0x32, // Usage (In Range) 32
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0x95, 0x01, // Report Count (1) 34
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0x81, 0x02, // Input (Data,Var,Abs) 36
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0x95, 0x02, // Report Count (2) 38
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0x81, 0x03, // Input (Cnst,Var,Abs) 40
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0x75, 0x10, // Report Size (16) 42
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0x95, 0x01, // Report Count (1) 44
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0x35, 0x00, // Physical Minimum (0) 46
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0xa4, // Push 48
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0x05, 0x01, // Usage Page (Generic Desktop) 49
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0x09, 0x30, // Usage (X) 51
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0x65, 0x13, // Unit (EnglishLinear: in) 53
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0x55, 0x0d, // Unit Exponent (-3) 55
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0x46, 0xf0, 0x50, // Physical Maximum (20720) 57
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0x26, 0xff, 0x7f, // Logical Maximum (32767) 60
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0x81, 0x02, // Input (Data,Var,Abs) 63
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0x09, 0x31, // Usage (Y) 65
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0x46, 0x91, 0x2d, // Physical Maximum (11665) 67
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0x26, 0xff, 0x7f, // Logical Maximum (32767) 70
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0x81, 0x02, // Input (Data,Var,Abs) 73
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0xb4, // Pop 75
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0x09, 0x30, // Usage (Tip Pressure) 76
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0x45, 0x00, // Physical Maximum (0) 78
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0x26, 0xff, 0x1f, // Logical Maximum (8191) 80
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0x81, 0x42, // Input (Data,Var,Abs,Null) 83
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0x09, 0x3d, // Usage (X Tilt) 85
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0x15, 0x81, // Logical Minimum (-127) 87
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0x25, 0x7f, // Logical Maximum (127) 89
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0x75, 0x08, // Report Size (8) 91
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0x95, 0x01, // Report Count (1) 93
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0x81, 0x02, // Input (Data,Var,Abs) 95
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0x09, 0x3e, // Usage (Y Tilt) 97
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0x15, 0x81, // Logical Minimum (-127) 99
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0x25, 0x7f, // Logical Maximum (127) 101
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0x81, 0x02, // Input (Data,Var,Abs) 103
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0xc0, // End Collection 105
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0xc0, // End Collection 106
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};
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#define TIP_SWITCH BIT(0)
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#define BARREL_SWITCH BIT(1)
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#define ERASER BIT(2)
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/* padding BIT(3) */
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/* padding BIT(4) */
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#define IN_RANGE BIT(5)
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/* padding BIT(6) */
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/* padding BIT(7) */
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#define U16(index) (data[index] | (data[index + 1] << 8))
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SEC(HID_BPF_RDESC_FIXUP)
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int BPF_PROG(hid_fix_rdesc_xppen_artist24, struct hid_bpf_ctx *hctx)
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{
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__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);
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if (!data)
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return 0; /* EPERM check */
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__builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc));
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return sizeof(fixed_rdesc);
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}
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static __u8 prev_state = 0;
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/*
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* There are a few cases where the device is sending wrong event
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* sequences, all related to the second button (the pen doesn't
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* have an eraser switch on the tail end):
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*
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* whenever the second button gets pressed or released, an
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* out-of-proximity event is generated and then the firmware
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* compensate for the missing state (and the firmware uses
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* eraser for that button):
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*
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* - if the pen is in range, an extra out-of-range is sent
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* when the second button is pressed/released:
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* // Pen is in range
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* E: InRange
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*
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* // Second button is pressed
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* E:
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* E: Eraser InRange
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*
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* // Second button is released
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* E:
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* E: InRange
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*
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* This case is ignored by this filter, it's "valid"
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* and userspace knows how to deal with it, there are just
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* a few out-of-prox events generated, but the user doesn´t
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* see them.
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*
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* - if the pen is in contact, 2 extra events are added when
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* the second button is pressed/released: an out of range
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* and an in range:
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*
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* // Pen is in contact
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* E: TipSwitch InRange
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*
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* // Second button is pressed
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* E: <- false release, needs to be filtered out
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* E: Eraser InRange <- false release, needs to be filtered out
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* E: TipSwitch Eraser InRange
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*
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* // Second button is released
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* E: <- false release, needs to be filtered out
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* E: InRange <- false release, needs to be filtered out
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* E: TipSwitch InRange
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*
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*/
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SEC(HID_BPF_DEVICE_EVENT)
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int BPF_PROG(xppen_24_fix_eraser, struct hid_bpf_ctx *hctx)
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{
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__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */);
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__u8 current_state, changed_state;
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bool prev_tip;
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if (!data)
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return 0; /* EPERM check */
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current_state = data[1];
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/* if the state is identical to previously, early return */
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if (current_state == prev_state)
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return 0;
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prev_tip = !!(prev_state & TIP_SWITCH);
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/*
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* Illegal transition: pen is in range with the tip pressed, and
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* it goes into out of proximity.
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*
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* Ideally we should hold the event, start a timer and deliver it
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* only if the timer ends, but we are not capable of that now.
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*
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* And it doesn't matter because when we are in such cases, this
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* means we are detecting a false release.
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*/
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if ((current_state & IN_RANGE) == 0) {
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if (prev_tip)
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return HID_IGNORE_EVENT;
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return 0;
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}
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/*
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* XOR to only set the bits that have changed between
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* previous and current state
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*/
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changed_state = prev_state ^ current_state;
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/* Store the new state for future processing */
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prev_state = current_state;
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/*
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* We get both a tipswitch and eraser change in the same HID report:
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* this is not an authorized transition and is unlikely to happen
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* in real life.
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* This is likely to be added by the firmware to emulate the
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* eraser mode so we can skip the event.
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*/
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if ((changed_state & (TIP_SWITCH | ERASER)) == (TIP_SWITCH | ERASER)) /* we get both a tipswitch and eraser change at the same time */
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return HID_IGNORE_EVENT;
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return 0;
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}
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HID_BPF_OPS(xppen_artist_24) = {
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.hid_rdesc_fixup = (void *)hid_fix_rdesc_xppen_artist24,
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.hid_device_event = (void *)xppen_24_fix_eraser,
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};
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SEC("syscall")
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int probe(struct hid_bpf_probe_args *ctx)
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{
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/*
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* The device exports 3 interfaces.
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*/
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ctx->retval = ctx->rdesc_size != 107;
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if (ctx->retval)
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ctx->retval = -EINVAL;
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/* ensure the kernel isn't fixed already */
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if (ctx->rdesc[17] != 0x45) /* Eraser */
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ctx->retval = -EINVAL;
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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