Input: Add IBM Operation Panel driver

Add a driver to get the button events from the panel and provide
them to userspace with the input subsystem. The panel is
connected with I2C and controls the bus, so the driver registers
as an I2C slave device.

Signed-off-by: Eddie James <[e-mail]>
Reviewed-by: Joel Stanley <[e-mail]>
Reviewed-by: Wolfram Sang <[e-mail]> # I2C slave parts
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

MAINTAINERS

···
 L:	[e-mail]
 S:	Maintained
 F:	Documentation/devicetree/bindings/input/ibm,op-panel.yaml
+F:	drivers/input/misc/ibm-panel.c
 
 IBM Power 842 compression accelerator
 M:	Haren Myneni <[e-mail]>

drivers/input/misc/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called adxl34x-spi.
 
+config INPUT_IBM_PANEL
+	tristate "IBM Operation Panel driver"
+	depends on I2C && I2C_SLAVE
+	help
+	  Say Y here if you have an IBM Operation Panel connected to your system
+	  over I2C. The panel is typically connected only to a system's service
+	  processor (BMC).
+
+	  If unsure, say N.
+
+	  The Operation Panel is a controller with some buttons and an LCD
+	  display that allows someone with physical access to the system to
+	  perform various administrative tasks. This driver only supports the part
+	  of the controller that sends commands to the system.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called ibm-panel.
+
 config INPUT_IMS_PCU
 	tristate "IMS Passenger Control Unit driver"
 	depends on USB

drivers/input/misc/Makefile

···
 obj-$(CONFIG_INPUT_GPIO_VIBRA)		+= gpio-vibra.o
 obj-$(CONFIG_INPUT_HISI_POWERKEY)	+= hisi_powerkey.o
 obj-$(CONFIG_HP_SDC_RTC)		+= hp_sdc_rtc.o
+obj-$(CONFIG_INPUT_IBM_PANEL)		+= ibm-panel.o
 obj-$(CONFIG_INPUT_IMS_PCU)		+= ims-pcu.o
 obj-$(CONFIG_INPUT_IQS269A)		+= iqs269a.o
 obj-$(CONFIG_INPUT_IQS626A)		+= iqs626a.o

drivers/input/misc/ibm-panel.c

···
+// 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)
+{
+	unsigned long flags;
+	struct ibm_panel *panel = i2c_get_clientdata(client);
+
+	dev_dbg(&panel->input->dev, "event: %u data: %02x\n", event, *val);
+
+	spin_lock_irqsave(&panel->lock, flags);
+
+	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;
+	}
+
+	spin_unlock_irqrestore(&panel->lock, flags);
+
+	return 0;
+}
+
+static int ibm_panel_probe(struct i2c_client *client,
+			   const struct i2c_device_id *id)
+{
+	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" },
+	{ }
+};
+
+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 <[e-mail]>");
+MODULE_DESCRIPTION("IBM Operation Panel Driver");
+MODULE_LICENSE("GPL");