// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) IBM Corporation 2020
 */

#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/input.h>
#include <linux/kernel.h>
#include <linux/limits.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/spinlock.h>

#define DEVICE_NAME  "ibm-panel"
#define PANEL_KEYCODES_COUNT 3

struct ibm_panel {
 u8 idx;
 u8 command[11];
 u32 keycodes[PANEL_KEYCODES_COUNT];
 spinlock_t lock; /* protects writes to idx and command */
 struct input_dev *input;
};

static u8 ibm_panel_calculate_checksum(struct ibm_panel *panel)
{
 u8 chksum;
 u16 sum = 0;
 unsigned int i;

 for (i = 0; i < sizeof(panel->command) - 1; ++i) {
  sum += panel->command[i];
  if (sum & 0xff00) {
   sum &= 0xff;
   sum++;
  }
 }

 chksum = sum & 0xff;
 chksum = ~chksum;
 chksum++;

 return chksum;
}

static void ibm_panel_process_command(struct ibm_panel *panel)
{
 u8 button;
 u8 chksum;

 if (panel->command[0] != 0xff && panel->command[1] != 0xf0) {
  dev_dbg(&panel->input->dev, "command invalid: %02x %02x\n",
   panel->command[0], panel->command[1]);
  return;
 }

 chksum = ibm_panel_calculate_checksum(panel);
 if (chksum != panel->command[sizeof(panel->command) - 1]) {
  dev_dbg(&panel->input->dev,
   "command failed checksum: %u != %u\n", chksum,
   panel->command[sizeof(panel->command) - 1]);
  return;
 }

 button = panel->command[2] & 0xf;
 if (button < PANEL_KEYCODES_COUNT) {
  input_report_key(panel->input, panel->keycodes[button],
     !(panel->command[2] & 0x80));
  input_sync(panel->input);
 } else {
  dev_dbg(&panel->input->dev, "unknown button %u\n",
   button);
 }
}

static int ibm_panel_i2c_slave_cb(struct i2c_client *client,
      enum i2c_slave_event event, u8 *val)
{
 struct ibm_panel *panel = i2c_get_clientdata(client);

 dev_dbg(&panel->input->dev, "event: %u data: %02x\n", event, *val);

 guard(spinlock_irqsave)(&panel->lock);

 switch (event) {
 case I2C_SLAVE_STOP:
  if (panel->idx == sizeof(panel->command))
   ibm_panel_process_command(panel);
  else
   dev_dbg(&panel->input->dev,
    "command incorrect size %u\n", panel->idx);
  fallthrough;
 case I2C_SLAVE_WRITE_REQUESTED:
  panel->idx = 0;
  break;
 case I2C_SLAVE_WRITE_RECEIVED:
  if (panel->idx < sizeof(panel->command))
   panel->command[panel->idx++] = *val;
  else
   /*
    * The command is too long and therefore invalid, so set the index
    * to it's largest possible value. When a STOP is finally received,
    * the command will be rejected upon processing.
 */
   panel->idx = U8_MAX;
  break;
 case I2C_SLAVE_READ_REQUESTED:
 case I2C_SLAVE_READ_PROCESSED:
  *val = 0xff;
  break;
 default:
  break;
 }

 return 0;
}

static int ibm_panel_probe(struct i2c_client *client)
{
 struct ibm_panel *panel;
 int i;
 int error;

 panel = devm_kzalloc(&client->dev, sizeof(*panel), GFP_KERNEL);
 if (!panel)
  return -ENOMEM;

 spin_lock_init(&panel->lock);

 panel->input = devm_input_allocate_device(&client->dev);
 if (!panel->input)
  return -ENOMEM;

 panel->input->name = client->name;
 panel->input->id.bustype = BUS_I2C;

 error = device_property_read_u32_array(&client->dev,
            "linux,keycodes",
            panel->keycodes,
            PANEL_KEYCODES_COUNT);
 if (error) {
  /*
   * Use gamepad buttons as defaults for compatibility with
   * existing applications.
 */
  panel->keycodes[0] = BTN_NORTH;
  panel->keycodes[1] = BTN_SOUTH;
  panel->keycodes[2] = BTN_SELECT;
 }

 for (i = 0; i < PANEL_KEYCODES_COUNT; ++i)
  input_set_capability(panel->input, EV_KEY, panel->keycodes[i]);

 error = input_register_device(panel->input);
 if (error) {
  dev_err(&client->dev,
   "Failed to register input device: %d\n", error);
  return error;
 }

 i2c_set_clientdata(client, panel);
 error = i2c_slave_register(client, ibm_panel_i2c_slave_cb);
 if (error) {
  dev_err(&client->dev,
   "Failed to register as i2c slave: %d\n", error);
  return error;
 }

 return 0;
}

static void ibm_panel_remove(struct i2c_client *client)
{
 i2c_slave_unregister(client);
}

static const struct of_device_id ibm_panel_match[] = {
 { .compatible = "ibm,op-panel" },
 { }
};
MODULE_DEVICE_TABLE(of, ibm_panel_match);

static struct i2c_driver ibm_panel_driver = {
 .driver = {
  .name = DEVICE_NAME,
  .of_match_table = ibm_panel_match,
 },
 .probe = ibm_panel_probe,
 .remove = ibm_panel_remove,
};
module_i2c_driver(ibm_panel_driver);

MODULE_AUTHOR("Eddie James <eajames@linux.ibm.com>");
MODULE_DESCRIPTION("IBM Operation Panel Driver");
MODULE_LICENSE("GPL");