Input: add driver for power button on Dell Wyse 3020

This adds support for the power button attached to the Embedded Controller
on a Dell Wyse 3020 "Ariel" board.

The Embedded Controller's SPI interface is actually capable sending and
receiving the PS/2 keyboard and mouse protocol data, which looks like
a good fit for a serio driver. Howerver, I don't know of any machines where
this is actually used.

My board only has a single power button and no way to connect an actual
keyboard or a mouse. Using the atkbd driver with serio would be an overkill
and would be inconvenient for the userspace. Therefore this driver
registers an input device that is only capable of reporting the power
button presses and releases.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20201201083533.1724287-3-lkundrak@v3.sk
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/Kconfig

@@ -73,6 +73,17 @@ config INPUT_AD714X_SPI
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad714x-spi.
 
+config INPUT_ARIEL_PWRBUTTON
+	tristate "Dell Wyse 3020 Power Button Driver"
+	depends on SPI
+	depends on MACH_MMP3_DT || COMPILE_TEST
+	help
+	  Say Y to enable support for reporting power button status on
+	  on Dell Wyse 3020 ("Ariel") thin client.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called ariel-pwrbutton.
+
 config INPUT_ARIZONA_HAPTICS
 	tristate "Arizona haptics support"
 	depends on MFD_ARIZONA && SND_SOC

drivers/input/misc/Makefile

@@ -15,6 +15,7 @@ obj-$(CONFIG_INPUT_ADXL34X)		+= adxl34x.o
 obj-$(CONFIG_INPUT_ADXL34X_I2C)		+= adxl34x-i2c.o
 obj-$(CONFIG_INPUT_ADXL34X_SPI)		+= adxl34x-spi.o
 obj-$(CONFIG_INPUT_APANEL)		+= apanel.o
+obj-$(CONFIG_INPUT_ARIEL_PWRBUTTON)	+= ariel-pwrbutton.o
 obj-$(CONFIG_INPUT_ARIZONA_HAPTICS)	+= arizona-haptics.o
 obj-$(CONFIG_INPUT_ATI_REMOTE2)		+= ati_remote2.o
 obj-$(CONFIG_INPUT_ATLAS_BTNS)		+= atlas_btns.o

drivers/input/misc/ariel-pwrbutton.c

@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: BSD-2-Clause OR GPL-2.0-or-later
+/*
+ * Dell Wyse 3020 a.k.a. "Ariel" Power Button Driver
+ *
+ * Copyright (C) 2020 Lubomir Rintel
+ */
+
+#include <linux/device.h>
+#include <linux/gfp.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+
+#define RESP_COUNTER(response)	(response.header & 0x3)
+#define RESP_SIZE(response)	((response.header >> 2) & 0x3)
+#define RESP_TYPE(response)	((response.header >> 4) & 0xf)
+
+struct ec_input_response {
+	u8 reserved;
+	u8 header;
+	u8 data[3];
+} __packed;
+
+struct ariel_pwrbutton {
+	struct spi_device *client;
+	struct input_dev *input;
+	u8 msg_counter;
+};
+
+static int ec_input_read(struct ariel_pwrbutton *priv,
+			 struct ec_input_response *response)
+{
+	u8 read_request[] = { 0x00, 0x5a, 0xa5, 0x00, 0x00 };
+	struct spi_device *spi = priv->client;
+	struct spi_transfer t = {
+		.tx_buf = read_request,
+		.rx_buf = response,
+		.len = sizeof(read_request),
+	};
+
+	compiletime_assert(sizeof(read_request) == sizeof(*response),
+			   "SPI xfer request/response size mismatch");
+
+	return spi_sync_transfer(spi, &t, 1);
+}
+
+static irqreturn_t ec_input_interrupt(int irq, void *dev_id)
+{
+	struct ariel_pwrbutton *priv = dev_id;
+	struct spi_device *spi = priv->client;
+	struct ec_input_response response;
+	int error;
+	int i;
+
+	error = ec_input_read(priv, &response);
+	if (error < 0) {
+		dev_err(&spi->dev, "EC read failed: %d\n", error);
+		goto out;
+	}
+
+	if (priv->msg_counter == RESP_COUNTER(response)) {
+		dev_warn(&spi->dev, "No new data to read?\n");
+		goto out;
+	}
+
+	priv->msg_counter = RESP_COUNTER(response);
+
+	if (RESP_TYPE(response) != 0x3 && RESP_TYPE(response) != 0xc) {
+		dev_dbg(&spi->dev, "Ignoring message that's not kbd data\n");
+		goto out;
+	}
+
+	for (i = 0; i < RESP_SIZE(response); i++) {
+		switch (response.data[i]) {
+		case 0x74:
+			input_report_key(priv->input, KEY_POWER, 1);
+			input_sync(priv->input);
+			break;
+		case 0xf4:
+			input_report_key(priv->input, KEY_POWER, 0);
+			input_sync(priv->input);
+			break;
+		default:
+			dev_dbg(&spi->dev, "Unknown scan code: %02x\n",
+				response.data[i]);
+		}
+	}
+
+out:
+	return IRQ_HANDLED;
+}
+
+static int ariel_pwrbutton_probe(struct spi_device *spi)
+{
+	struct ec_input_response response;
+	struct ariel_pwrbutton *priv;
+	int error;
+
+	if (!spi->irq) {
+		dev_err(&spi->dev, "Missing IRQ.\n");
+		return -EINVAL;
+	}
+
+	priv = devm_kzalloc(&spi->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->client = spi;
+	spi_set_drvdata(spi, priv);
+
+	priv->input = devm_input_allocate_device(&spi->dev);
+	if (!priv->input)
+		return -ENOMEM;
+	priv->input->name = "Power Button";
+	priv->input->dev.parent = &spi->dev;
+	input_set_capability(priv->input, EV_KEY, KEY_POWER);
+	error = input_register_device(priv->input);
+	if (error) {
+		dev_err(&spi->dev, "error registering input device: %d\n", error);
+		return error;
+	}
+
+	error = ec_input_read(priv, &response);
+	if (error < 0) {
+		dev_err(&spi->dev, "EC read failed: %d\n", error);
+		return error;
+	}
+	priv->msg_counter = RESP_COUNTER(response);
+
+	error = devm_request_threaded_irq(&spi->dev, spi->irq, NULL,
+					  ec_input_interrupt,
+					  IRQF_ONESHOT,
+					  "Ariel EC Input", priv);
+
+	if (error) {
+		dev_err(&spi->dev, "Failed to request IRQ %d: %d\n",
+			spi->irq, error);
+		return error;
+	}
+
+	return 0;
+}
+
+static const struct of_device_id ariel_pwrbutton_of_match[] = {
+	{ .compatible = "dell,wyse-ariel-ec-input" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ariel_pwrbutton_of_match);
+
+static const struct spi_device_id ariel_pwrbutton_id_table[] = {
+	{ "wyse-ariel-ec-input", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, ariel_pwrbutton_id_table);
+
+static struct spi_driver ariel_pwrbutton_driver = {
+	.driver = {
+		.name = "dell-wyse-ariel-ec-input",
+		.of_match_table = ariel_pwrbutton_of_match,
+	},
+	.probe = ariel_pwrbutton_probe,
+};
+module_spi_driver(ariel_pwrbutton_driver);
+
+MODULE_AUTHOR("Lubomir Rintel <lkundrak@v3.sk>");
+MODULE_DESCRIPTION("Dell Wyse 3020 Power Button Input Driver");
+MODULE_LICENSE("Dual BSD/GPL");