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 <geert+renesas@glider.be>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

3 files changed, 161 insertions, 0 deletions

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index ade542c5bfd8..e6d9e329a380 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -802,6 +802,12 @@ config SPI_SLAVE_TIME
           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
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index fb078693dbe4..1d7923e8c63b 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -108,3 +108,4 @@ obj-$(CONFIG_SPI_ZYNQMP_GQSPI)		+= spi-zynqmp-gqspi.o
 
 # SPI slave protocol handlers
 obj-$(CONFIG_SPI_SLAVE_TIME)            += spi-slave-time.o
+obj-$(CONFIG_SPI_SLAVE_SYSTEM_CONTROL)  += spi-slave-system-control.o
diff --git a/drivers/spi/spi-slave-system-control.c b/drivers/spi/spi-slave-system-control.c
new file mode 100644
index 000000000000..c0257e937995
--- /dev/null
+++ b/drivers/spi/spi-slave-system-control.c
@@ -0,0 +1,154 @@
+/*
+ * 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 <geert+renesas@glider.be>");
+MODULE_DESCRIPTION("SPI slave handler controlling system state");
+MODULE_LICENSE("GPL v2");