diff options
Diffstat (limited to 'drivers/hid/bpf/progs/Wacom__ArtPen.bpf.c')
| -rw-r--r-- | drivers/hid/bpf/progs/Wacom__ArtPen.bpf.c | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/drivers/hid/bpf/progs/Wacom__ArtPen.bpf.c b/drivers/hid/bpf/progs/Wacom__ArtPen.bpf.c new file mode 100644 index 000000000000..dc05aa48faa7 --- /dev/null +++ b/drivers/hid/bpf/progs/Wacom__ArtPen.bpf.c @@ -0,0 +1,173 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright (c) 2024 Benjamin Tissoires + */ + +#include "vmlinux.h" +#include "hid_bpf.h" +#include "hid_bpf_helpers.h" +#include <bpf/bpf_tracing.h> + +#define VID_WACOM 0x056a +#define ART_PEN_ID 0x0804 +#define PID_INTUOS_PRO_2_M 0x0357 + +HID_BPF_CONFIG( + HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_WACOM, PID_INTUOS_PRO_2_M) +); + +/* + * This filter is here for the Art Pen stylus only: + * - when used on some Wacom devices (see the list of attached PIDs), this pen + * reports pressure every other events. + * - to solve that, given that we know that the next event will be the same as + * the current one, we can emulate a smoother pressure reporting by reporting + * the mean of the previous value and the current one. + * + * We are effectively delaying the pressure by one event every other event, but + * that's less of an annoyance compared to the chunkiness of the reported data. + * + * For example, let's assume the following set of events: + * <Tip switch 0> <X 0> <Y 0> <Pressure 0 > <Tooltype 0x0804> + * <Tip switch 1> <X 1> <Y 1> <Pressure 100 > <Tooltype 0x0804> + * <Tip switch 1> <X 2> <Y 2> <Pressure 100 > <Tooltype 0x0804> + * <Tip switch 1> <X 3> <Y 3> <Pressure 200 > <Tooltype 0x0804> + * <Tip switch 1> <X 4> <Y 4> <Pressure 200 > <Tooltype 0x0804> + * <Tip switch 0> <X 5> <Y 5> <Pressure 0 > <Tooltype 0x0804> + * + * The filter will report: + * <Tip switch 0> <X 0> <Y 0> <Pressure 0 > <Tooltype 0x0804> + * <Tip switch 1> <X 1> <Y 1> <Pressure * 50*> <Tooltype 0x0804> + * <Tip switch 1> <X 2> <Y 2> <Pressure 100 > <Tooltype 0x0804> + * <Tip switch 1> <X 3> <Y 3> <Pressure *150*> <Tooltype 0x0804> + * <Tip switch 1> <X 4> <Y 4> <Pressure 200 > <Tooltype 0x0804> + * <Tip switch 0> <X 5> <Y 5> <Pressure 0 > <Tooltype 0x0804> + * + */ + +struct wacom_params { + __u16 pid; + __u16 rdesc_len; + __u8 report_id; + __u8 report_len; + struct { + __u8 tip_switch; + __u8 pressure; + __u8 tool_type; + } offsets; +}; + +/* + * Multiple device can support the same stylus, so + * we need to know which device has which offsets + */ +static const struct wacom_params devices[] = { + { + .pid = PID_INTUOS_PRO_2_M, + .rdesc_len = 949, + .report_id = 16, + .report_len = 27, + .offsets = { + .tip_switch = 1, + .pressure = 8, + .tool_type = 25, + }, + }, +}; + +static struct wacom_params params = { 0 }; + +/* HID-BPF reports a 64 bytes chunk anyway, so this ensures + * the verifier to know we are addressing the memory correctly + */ +#define PEN_REPORT_LEN 64 + +/* only odd frames are modified */ +static bool odd; + +static __u16 prev_pressure; + +static inline void *get_bits(__u8 *data, unsigned int byte_offset) +{ + return data + byte_offset; +} + +static inline __u16 *get_u16(__u8 *data, unsigned int offset) +{ + return (__u16 *)get_bits(data, offset); +} + +static inline __u8 *get_u8(__u8 *data, unsigned int offset) +{ + return (__u8 *)get_bits(data, offset); +} + +SEC("fmod_ret/hid_bpf_device_event") +int BPF_PROG(artpen_pressure_interpolate, struct hid_bpf_ctx *hctx) +{ + __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, PEN_REPORT_LEN /* size */); + __u16 *pressure, *tool_type; + __u8 *tip_switch; + + if (!data) + return 0; /* EPERM check */ + + if (data[0] != params.report_id || + params.offsets.tip_switch >= PEN_REPORT_LEN || + params.offsets.pressure >= PEN_REPORT_LEN - 1 || + params.offsets.tool_type >= PEN_REPORT_LEN - 1) + return 0; /* invalid report or parameters */ + + tool_type = get_u16(data, params.offsets.tool_type); + if (*tool_type != ART_PEN_ID) + return 0; + + tip_switch = get_u8(data, params.offsets.tip_switch); + if ((*tip_switch & 0x01) == 0) { + prev_pressure = 0; + odd = true; + return 0; + } + + pressure = get_u16(data, params.offsets.pressure); + + if (odd) + *pressure = (*pressure + prev_pressure) / 2; + + prev_pressure = *pressure; + odd = !odd; + + return 0; +} + +SEC("syscall") +int probe(struct hid_bpf_probe_args *ctx) +{ + struct hid_bpf_ctx *hid_ctx; + __u16 pid; + int i; + + /* get a struct hid_device to access the actual pid of the device */ + hid_ctx = hid_bpf_allocate_context(ctx->hid); + if (!hid_ctx) { + ctx->retval = -ENODEV; + return -1; /* EPERM check */ + } + pid = hid_ctx->hid->product; + + ctx->retval = -EINVAL; + + /* Match the given device with the list of known devices */ + for (i = 0; i < ARRAY_SIZE(devices); i++) { + const struct wacom_params *device = &devices[i]; + + if (device->pid == pid && device->rdesc_len == ctx->rdesc_size) { + params = *device; + ctx->retval = 0; + } + } + + hid_bpf_release_context(hid_ctx); + return 0; +} + +char _license[] SEC("license") = "GPL"; |