spi: slave: Add SPI slave handler reporting uptime at previous message

Add an example SPI slave handler responding with the uptime at the time
of reception of the last SPI message.

This can be used by an external microcontroller as a dead man's switch.

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, 136 insertions, 0 deletions

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index df8ddec24b5d..ade542c5bfd8 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -796,6 +796,12 @@ config SPI_SLAVE
 
 if SPI_SLAVE
 
+config SPI_SLAVE_TIME
+        tristate "SPI slave handler reporting boot up time"
+        help
+          SPI slave handler responding with the time of reception of the last
+          SPI message.
+
 endif # SPI_SLAVE
 
 endif # SPI
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index e50852c6fcb8..fb078693dbe4 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -107,3 +107,4 @@ obj-$(CONFIG_SPI_XTENSA_XTFPGA)		+= spi-xtensa-xtfpga.o
 obj-$(CONFIG_SPI_ZYNQMP_GQSPI)          += spi-zynqmp-gqspi.o
 
 # SPI slave protocol handlers
+obj-$(CONFIG_SPI_SLAVE_TIME)            += spi-slave-time.o
diff --git a/drivers/spi/spi-slave-time.c b/drivers/spi/spi-slave-time.c
new file mode 100644
index 000000000000..f2e07a392d68
--- /dev/null
+++ b/drivers/spi/spi-slave-time.c
@@ -0,0 +1,129 @@
+/*
+ * SPI slave handler reporting uptime at reception of previous SPI message
+ *
+ * This SPI slave handler sends the time of reception of the last SPI message
+ * as two 32-bit unsigned integers in binary format and in network byte order,
+ * representing the number of seconds and fractional seconds (in microseconds)
+ * since boot up.
+ *
+ * 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):
+ *
+ *   # spidev_test -D /dev/spidev2.0 -p dummy-8B
+ *   spi mode: 0x0
+ *   bits per word: 8
+ *   max speed: 500000 Hz (500 KHz)
+ *   RX | 00 00 04 6D 00 09 5B BB ...
+ *              ^^^^^    ^^^^^^^^
+ *              seconds  microseconds
+ */
+
+#include <linux/completion.h>
+#include <linux/module.h>
+#include <linux/sched/clock.h>
+#include <linux/spi/spi.h>
+
+
+struct spi_slave_time_priv {
+        struct spi_device *spi;
+        struct completion finished;
+        struct spi_transfer xfer;
+        struct spi_message msg;
+        __be32 buf[2];
+};
+
+static int spi_slave_time_submit(struct spi_slave_time_priv *priv);
+
+static void spi_slave_time_complete(void *arg)
+{
+        struct spi_slave_time_priv *priv = arg;
+        int ret;
+
+        ret = priv->msg.status;
+        if (ret)
+                goto terminate;
+
+        ret = spi_slave_time_submit(priv);
+        if (ret)
+                goto terminate;
+
+        return;
+
+terminate:
+        dev_info(&priv->spi->dev, "Terminating\n");
+        complete(&priv->finished);
+}
+
+static int spi_slave_time_submit(struct spi_slave_time_priv *priv)
+{
+        u32 rem_us;
+        int ret;
+        u64 ts;
+
+        ts = local_clock();
+        rem_us = do_div(ts, 1000000000) / 1000;
+
+        priv->buf[0] = cpu_to_be32(ts);
+        priv->buf[1] = cpu_to_be32(rem_us);
+
+        spi_message_init_with_transfers(&priv->msg, &priv->xfer, 1);
+
+        priv->msg.complete = spi_slave_time_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_time_probe(struct spi_device *spi)
+{
+        struct spi_slave_time_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.tx_buf = priv->buf;
+        priv->xfer.len = sizeof(priv->buf);
+
+        ret = spi_slave_time_submit(priv);
+        if (ret)
+                return ret;
+
+        spi_set_drvdata(spi, priv);
+        return 0;
+}
+
+static int spi_slave_time_remove(struct spi_device *spi)
+{
+        struct spi_slave_time_priv *priv = spi_get_drvdata(spi);
+
+        spi_slave_abort(spi);
+        wait_for_completion(&priv->finished);
+        return 0;
+}
+
+static struct spi_driver spi_slave_time_driver = {
+        .driver = {
+                .name   = "spi-slave-time",
+        },
+        .probe          = spi_slave_time_probe,
+        .remove         = spi_slave_time_remove,
+};
+module_spi_driver(spi_slave_time_driver);
+
+MODULE_AUTHOR("Geert Uytterhoeven <geert+renesas@glider.be>");
+MODULE_DESCRIPTION("SPI slave reporting uptime at previous SPI message");
+MODULE_LICENSE("GPL v2");