spi: slave: Add SPI slave handler controlling system state

Add an example SPI slave handler to allow remote control of system
reboot, power off, halt, and suspend.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/Kconfig

···
 	  SPI slave handler responding with the time of reception of the last
 	  SPI message.
 
+config SPI_SLAVE_SYSTEM_CONTROL
+	tristate "SPI slave handler controlling system state"
+	help
+	  SPI slave handler to allow remote control of system reboot, power
+	  off, halt, and suspend.
+
 endif # SPI_SLAVE
 
 endif # SPI

drivers/spi/Makefile

···
 
 # SPI slave protocol handlers
 obj-$(CONFIG_SPI_SLAVE_TIME)		+= spi-slave-time.o
+obj-$(CONFIG_SPI_SLAVE_SYSTEM_CONTROL)	+= spi-slave-system-control.o

drivers/spi/spi-slave-system-control.c

···
+/*
+ * SPI slave handler controlling system state
+ *
+ * This SPI slave handler allows remote control of system reboot, power off,
+ * halt, and suspend.
+ *
+ * Copyright (C) 2016-2017 Glider bvba
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Usage (assuming /dev/spidev2.0 corresponds to the SPI master on the remote
+ * system):
+ *
+ *   # reboot='\x7c\x50'
+ *   # poweroff='\x71\x3f'
+ *   # halt='\x38\x76'
+ *   # suspend='\x1b\x1b'
+ *   # spidev_test -D /dev/spidev2.0 -p $suspend # or $reboot, $poweroff, $halt
+ */
+
+#include <linux/completion.h>
+#include <linux/module.h>
+#include <linux/reboot.h>
+#include <linux/suspend.h>
+#include <linux/spi/spi.h>
+
+/*
+ * The numbers are chosen to display something human-readable on two 7-segment
+ * displays connected to two 74HC595 shift registers
+ */
+#define CMD_REBOOT	0x7c50	/* rb */
+#define CMD_POWEROFF	0x713f	/* OF */
+#define CMD_HALT	0x3876	/* HL */
+#define CMD_SUSPEND	0x1b1b	/* ZZ */
+
+struct spi_slave_system_control_priv {
+	struct spi_device *spi;
+	struct completion finished;
+	struct spi_transfer xfer;
+	struct spi_message msg;
+	__be16 cmd;
+};
+
+static
+int spi_slave_system_control_submit(struct spi_slave_system_control_priv *priv);
+
+static void spi_slave_system_control_complete(void *arg)
+{
+	struct spi_slave_system_control_priv *priv = arg;
+	u16 cmd;
+	int ret;
+
+	if (priv->msg.status)
+		goto terminate;
+
+	cmd = be16_to_cpu(priv->cmd);
+	switch (cmd) {
+	case CMD_REBOOT:
+		dev_info(&priv->spi->dev, "Rebooting system...\n");
+		kernel_restart(NULL);
+
+	case CMD_POWEROFF:
+		dev_info(&priv->spi->dev, "Powering off system...\n");
+		kernel_power_off();
+		break;
+
+	case CMD_HALT:
+		dev_info(&priv->spi->dev, "Halting system...\n");
+		kernel_halt();
+		break;
+
+	case CMD_SUSPEND:
+		dev_info(&priv->spi->dev, "Suspending system...\n");
+		pm_suspend(PM_SUSPEND_MEM);
+		break;
+
+	default:
+		dev_warn(&priv->spi->dev, "Unknown command 0x%x\n", cmd);
+		break;
+	}
+
+	ret = spi_slave_system_control_submit(priv);
+	if (ret)
+		goto terminate;
+
+	return;
+
+terminate:
+	dev_info(&priv->spi->dev, "Terminating\n");
+	complete(&priv->finished);
+}
+
+static
+int spi_slave_system_control_submit(struct spi_slave_system_control_priv *priv)
+{
+	int ret;
+
+	spi_message_init_with_transfers(&priv->msg, &priv->xfer, 1);
+
+	priv->msg.complete = spi_slave_system_control_complete;
+	priv->msg.context = priv;
+
+	ret = spi_async(priv->spi, &priv->msg);
+	if (ret)
+		dev_err(&priv->spi->dev, "spi_async() failed %d\n", ret);
+
+	return ret;
+}
+
+static int spi_slave_system_control_probe(struct spi_device *spi)
+{
+	struct spi_slave_system_control_priv *priv;
+	int ret;
+
+	priv = devm_kzalloc(&spi->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->spi = spi;
+	init_completion(&priv->finished);
+	priv->xfer.rx_buf = &priv->cmd;
+	priv->xfer.len = sizeof(priv->cmd);
+
+	ret = spi_slave_system_control_submit(priv);
+	if (ret)
+		return ret;
+
+	spi_set_drvdata(spi, priv);
+	return 0;
+}
+
+static int spi_slave_system_control_remove(struct spi_device *spi)
+{
+	struct spi_slave_system_control_priv *priv = spi_get_drvdata(spi);
+
+	spi_slave_abort(spi);
+	wait_for_completion(&priv->finished);
+	return 0;
+}
+
+static struct spi_driver spi_slave_system_control_driver = {
+	.driver = {
+		.name	= "spi-slave-system-control",
+	},
+	.probe		= spi_slave_system_control_probe,
+	.remove		= spi_slave_system_control_remove,
+};
+module_spi_driver(spi_slave_system_control_driver);
+
+MODULE_AUTHOR("Geert Uytterhoeven <[e-mail]>");
+MODULE_DESCRIPTION("SPI slave handler controlling system state");
+MODULE_LICENSE("GPL v2");