text: // SPDX-License-Identifier: GPL-2.0-or-later
  /*
   *  Force feedback support for Logitech Flight System G940
   *
   *  Copyright (c) 2009 Gary Stein <LordCnidarian@gmail.com>
   */
  
  /*
   */
  
  
  #include <linux/input.h>
  #include <linux/hid.h>
  
  #include "hid-lg.h"
  
  /*
   * G940 Theory of Operation (from experimentation)
   *
   * There are 63 fields (only 3 of them currently used)
   * 0 - seems to be command field
   * 1 - 30 deal with the x axis
   * 31 -60 deal with the y axis
   *
   * Field 1 is x axis constant force
   * Field 31 is y axis constant force
   *
   * other interesting fields 1,2,3,4 on x axis
   * (same for 31,32,33,34 on y axis)
   *
   * 0 0 127 127 makes the joystick autocenter hard
   *
   * 127 0 127 127 makes the joystick loose on the right,
   * but stops all movemnt left
   *
   * -127 0 -127 -127 makes the joystick loose on the left,
   * but stops all movement right
   *
   * 0 0 -127 -127 makes the joystick rattle very hard
   *
   * I'm sure these are effects that I don't know enough about them
   */
  
  struct lg3ff_device {
  	struct hid_report *report;
  };
  
  static int hid_lg3ff_play(struct input_dev *dev, void *data,
  			 struct ff_effect *effect)
  {
  	struct hid_device *hid = input_get_drvdata(dev);
  	struct list_head *report_list = &hid->report_enum[HID_OUTPUT_REPORT].report_list;
  	struct hid_report *report = list_entry(report_list->next, struct hid_report, list);
  	int x, y;
  
  /*
   * Available values in the field should always be 63, but we only use up to
   * 35. Instead, clear the entire area, however big it is.
   */
  	memset(report->field[0]->value, 0,
  	       sizeof(__s32) * report->field[0]->report_count);
  
  	switch (effect->type) {
  	case FF_CONSTANT:
  /*
   * Already clamped in ff_memless
   * 0 is center (different then other logitech)
   */
  		x = effect->u.ramp.start_level;
  		y = effect->u.ramp.end_level;
  
  		/* send command byte */
  		report->field[0]->value[0] = 0x51;
  
  /*
   * Sign backwards from other Force3d pro
   * which get recast here in two's complement 8 bits
   */
  		report->field[0]->value[1] = (unsigned char)(-x);
  		report->field[0]->value[31] = (unsigned char)(-y);
  
  		hid_hw_request(hid, report, HID_REQ_SET_REPORT);
  		break;
  	}
  	return 0;
  }
  static void hid_lg3ff_set_autocenter(struct input_dev *dev, u16 magnitude)
  {
  	struct hid_device *hid = input_get_drvdata(dev);
  	struct list_head *report_list = &hid->report_enum[HID_OUTPUT_REPORT].report_list;
  	struct hid_report *report = list_entry(report_list->next, struct hid_report, list);
  
  /*
   * Auto Centering probed from device
   * NOTE: deadman's switch on G940 must be covered
   * for effects to work
   */
  	report->field[0]->value[0] = 0x51;
  	report->field[0]->value[1] = 0x00;
  	report->field[0]->value[2] = 0x00;
  	report->field[0]->value[3] = 0x7F;
  	report->field[0]->value[4] = 0x7F;
  	report->field[0]->value[31] = 0x00;
  	report->field[0]->value[32] = 0x00;
  	report->field[0]->value[33] = 0x7F;
  	report->field[0]->value[34] = 0x7F;
  
  	hid_hw_request(hid, report, HID_REQ_SET_REPORT);
  }
  
  
  static const signed short ff3_joystick_ac[] = {
  	FF_CONSTANT,
  	FF_AUTOCENTER,
  	-1
  };
  
  int lg3ff_init(struct hid_device *hid)
  {
  	struct hid_input *hidinput;
  	struct input_dev *dev;
  	const signed short *ff_bits = ff3_joystick_ac;
  	int error;
  	int i;
  
  	if (list_empty(&hid->inputs)) {
  		hid_err(hid, "no inputs found\n");
  		return -ENODEV;
  	}
  	hidinput = list_entry(hid->inputs.next, struct hid_input, list);
  	dev = hidinput->input;
  
  	/* Check that the report looks ok */
  	if (!hid_validate_values(hid, HID_OUTPUT_REPORT, 0, 0, 35))
  		return -ENODEV;
  
  	/* Assume single fixed device G940 */
  	for (i = 0; ff_bits[i] >= 0; i++)
  		set_bit(ff_bits[i], dev->ffbit);
  
  	error = input_ff_create_memless(dev, NULL, hid_lg3ff_play);
  	if (error)
  		return error;
  
  	if (test_bit(FF_AUTOCENTER, dev->ffbit))
  		dev->ff->set_autocenter = hid_lg3ff_set_autocenter;
  
  	hid_info(hid, "Force feedback for Logitech Flight System G940 by Gary Stein <LordCnidarian@gmail.com>\n");
  	return 0;
  }
  
  