--- /dev/null
+// 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";
projects / linux-2.6-block.git / blobdiff