1 // SPDX-License-Identifier: GPL-2.0-only
18 /* Filled in by udev-hid-bpf */
26 /* How this BPF program works: the tablet has two modes, firmware mode and
27  * tablet mode. In firmware mode (out of the box) the tablet sends button events
28  * and the dial as keyboard combinations. In tablet mode it uses a vendor specific
30  * Depending on the mode some hid reports are never sent and the corresponding
33  * To switch the tablet use e.g.  https://github.com/whot/huion-switcher
36  * This BPF works for both modes. The huion-switcher tool sets the
37  * HUION_FIRMWARE_ID udev property - if that is set then we disable the firmware
39  * If that property is not set we fix all hidraw nodes so the tablet works in
40  * either mode though the drawback is that the device will show up twice if
58  * This rdesc does nothing until the tablet is switched to raw mode, see
59  * https://github.com/whot/huion-switcher
62  * Second hidraw node is the Pen. This one sends events until the tablet is
63  * switched to raw mode, then it's mute.
75  * # 0x09, 0x3c,          //     Usage (Invert)                        18 <-- has no Invert eraser
89  * # 0x55, 0x0d,          //     Unit Exponent (-3)                    46 <-- change to -2
90  * # 0x65, 0x33,          //     Unit (EnglishLinear: in³)             48 <-- change in³ to in
93  * # 0x46, 0x00, 0x08,    //     Physical Maximum (2048)               55 <-- invalid size
103  * # 0x09, 0x3d,          //     Usage (X Tilt)                        77 <-- No tilt reported
105  * # 0x15, 0x81,          //     Logical Minimum (-127)                81
115  * the tablet is switched to raw mode, then it's mute:
171 		// -- Byte 0 in report
177 			// Byte 1 in report - just exists so we get to be a tablet pad
184 			// Bytes 2/3 in report - just exists so we get to be a tablet pad
193 			LogicalRange_i8(-1, 1)
214 		// -- Byte 0 in report
218 			// -- Byte 1 in report
236 				UnitExponent(-1)
285 				UnitExponent(-1)
315 			Usage_Dig_BarrelSwitch	 // BTN_STYLUS, needed so we get to be a tablet pad
321 			// Bytes 2/3 - x/y just exist so we get to be a tablet pad
340 			LogicalRange_i8(-1, 1)
362 	__s32 rdesc_size = hctx->size;  in SEC()
374 				      sizeof(EXPECTED_FIRMWARE_ID) - 1) == 0;  in SEC()
393 	/* Always fix the vendor mode so the tablet will work even if nothing sets  in SEC()
394 	 * the udev property (e.g. huion-switcher run manually)  in SEC()
412 	/* Only sent if tablet is in default mode */  in SEC()
417 		 *   Button 1: 03 00 05 00 00 00 00 00 -> b  in SEC()
418 		 *   Button 2: 03 00 0c 00 00 00 00 00 -> i  in SEC()
419 		 *   Button 3: 03 00 08 00 00 00 00 00 -> e  in SEC()
420 		 *   Button 4: 03 01 16 00 00 00 00 00 -> Ctrl S  in SEC()
421 		 *   Button 5: 03 00 2c 00 00 00 00 00 -> space  in SEC()
422 		 *   Button 6: 03 05 1d 00 00 00 00 00 -> Ctrl Alt Z  in SEC()
424 		 *   Wheel down: 03 01 2d 00 00 00 00 00 -> Ctrl -  in SEC()
425 		 *   Wheel up:   03 01 2e 00 00 00 00 00 -> Ctrl =  in SEC()
452 			wheel = -1;  in SEC()
468 	/* Only sent if tablet is in raw mode */  in SEC()
497 			pad_report->report_id = PAD_REPORT_ID;  in SEC()
498 			pad_report->btn_stylus = 0;  in SEC()
499 			pad_report->x = 0;  in SEC()
500 			pad_report->y = 0;  in SEC()
501 			pad_report->buttons = last_button_state;  in SEC()
502 			pad_report->wheel = wheel;  in SEC()
521 	switch (ctx->rdesc_size) {  in probe()
525 		ctx->retval = 0;  in probe()
528 		ctx->retval = -EINVAL;  in probe()