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Subject[PATCH/RFC 4/6] spi: slave: Add SPI slave handler reporting boot up time
Date
Add an SPI slave handler responding with 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>
---
FIXME kthread_stop() hangs, as spi_write() is blocked on a completion
---
drivers/spi/Kconfig | 6 +++
drivers/spi/Makefile | 1 +
drivers/spi/spi-slave-time.c | 103 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 110 insertions(+)
create mode 100644 drivers/spi/spi-slave-time.c

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 00e990d91a715c0e..e9b2f48574464949 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -748,6 +748,12 @@ 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 71d02939080fb747..dc67b8f137e2ced0 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -99,3 +99,4 @@ 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 0000000000000000..3d606af318024573
--- /dev/null
+++ b/drivers/spi/spi-slave-time.c
@@ -0,0 +1,103 @@
+/*
+ * SPI slave handler reporting boot up time
+ *
+ * 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 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.
+ */
+
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/spi/spi.h>
+
+
+struct spi_slave_time_priv {
+ struct spi_device *spi;
+ struct task_struct *thread;
+};
+
+static int spi_slave_time_send(struct spi_device *spi)
+{
+ __be32 msg[2];
+ u32 rem_ns;
+ u64 ts;
+
+ ts = local_clock();
+ rem_ns = do_div(ts, 1000000000) / 1000;
+
+ msg[0] = cpu_to_be32(ts);
+ msg[1] = cpu_to_be32(rem_ns);
+
+ return spi_write(spi, &msg, sizeof(msg));
+}
+
+static int spi_slave_time_thread(void *data)
+{
+ struct spi_slave_time_priv *priv = data;
+ int error;
+
+ while (!kthread_should_stop()) {
+ error = spi_slave_time_send(priv->spi);
+ if (error)
+ pr_err("%s: SPI transfer failed %d\n", __func__, error);
+ }
+
+ return 0;
+}
+
+static int spi_slave_time_probe(struct spi_device *spi)
+{
+ struct spi_slave_time_priv *priv;
+ int ret;
+
+ /*
+ * bits_per_word cannot be configured in platform data
+ */
+ spi->bits_per_word = 8;
+
+ ret = spi_setup(spi);
+ if (ret < 0)
+ return ret;
+
+ priv = devm_kzalloc(&spi->dev, sizeof(*priv), GFP_KERNEL);
+ if (!priv)
+ return -ENOMEM;
+
+ priv->spi = spi;
+ priv->thread = kthread_run(spi_slave_time_thread, priv,
+ "spi-slave-time/%s", dev_name(&spi->dev));
+ if (IS_ERR(priv->thread))
+ return PTR_ERR(priv->thread);
+
+ 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);
+
+ /* FIXME Doesn't work, as spi_write() is blocked on a completion */
+ kthread_stop(priv->thread);
+ 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 boot up time");
+MODULE_LICENSE("GPL v2");
--
1.9.1
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