1/*
2 * SPI slave handler reporting uptime at reception of previous SPI message
3 *
4 * This SPI slave handler sends the time of reception of the last SPI message
5 * as two 32-bit unsigned integers in binary format and in network byte order,
6 * representing the number of seconds and fractional seconds (in microseconds)
7 * since boot up.
8 *
9 * Copyright (C) 2016-2017 Glider bvba
10 *
11 * This file is subject to the terms and conditions of the GNU General Public
12 * License.  See the file "COPYING" in the main directory of this archive
13 * for more details.
14 *
15 * Usage (assuming /dev/spidev2.0 corresponds to the SPI master on the remote
16 * system):
17 *
18 *   # spidev_test -D /dev/spidev2.0 -p dummy-8B
19 *   spi mode: 0x0
20 *   bits per word: 8
21 *   max speed: 500000 Hz (500 KHz)
22 *   RX | 00 00 04 6D 00 09 5B BB ...
23 *		^^^^^    ^^^^^^^^
24 *		seconds  microseconds
25 */
26
27#include <linux/completion.h>
28#include <linux/module.h>
29#include <linux/sched/clock.h>
30#include <linux/spi/spi.h>
31
32
33struct spi_slave_time_priv {
34	struct spi_device *spi;
35	struct completion finished;
36	struct spi_transfer xfer;
37	struct spi_message msg;
38	__be32 buf[2];
39};
40
41static int spi_slave_time_submit(struct spi_slave_time_priv *priv);
42
43static void spi_slave_time_complete(void *arg)
44{
45	struct spi_slave_time_priv *priv = arg;
46	int ret;
47
48	ret = priv->msg.status;
49	if (ret)
50		goto terminate;
51
52	ret = spi_slave_time_submit(priv);
53	if (ret)
54		goto terminate;
55
56	return;
57
58terminate:
59	dev_info(&priv->spi->dev, "Terminating\n");
60	complete(&priv->finished);
61}
62
63static int spi_slave_time_submit(struct spi_slave_time_priv *priv)
64{
65	u32 rem_us;
66	int ret;
67	u64 ts;
68
69	ts = local_clock();
70	rem_us = do_div(ts, 1000000000) / 1000;
71
72	priv->buf[0] = cpu_to_be32(ts);
73	priv->buf[1] = cpu_to_be32(rem_us);
74
75	spi_message_init_with_transfers(&priv->msg, &priv->xfer, 1);
76
77	priv->msg.complete = spi_slave_time_complete;
78	priv->msg.context = priv;
79
80	ret = spi_async(priv->spi, &priv->msg);
81	if (ret)
82		dev_err(&priv->spi->dev, "spi_async() failed %d\n", ret);
83
84	return ret;
85}
86
87static int spi_slave_time_probe(struct spi_device *spi)
88{
89	struct spi_slave_time_priv *priv;
90	int ret;
91
92	priv = devm_kzalloc(&spi->dev, sizeof(*priv), GFP_KERNEL);
93	if (!priv)
94		return -ENOMEM;
95
96	priv->spi = spi;
97	init_completion(&priv->finished);
98	priv->xfer.tx_buf = priv->buf;
99	priv->xfer.len = sizeof(priv->buf);
100
101	ret = spi_slave_time_submit(priv);
102	if (ret)
103		return ret;
104
105	spi_set_drvdata(spi, priv);
106	return 0;
107}
108
109static void spi_slave_time_remove(struct spi_device *spi)
110{
111	struct spi_slave_time_priv *priv = spi_get_drvdata(spi);
112
113	spi_slave_abort(spi);
114	wait_for_completion(&priv->finished);
115}
116
117static struct spi_driver spi_slave_time_driver = {
118	.driver = {
119		.name	= "spi-slave-time",
120	},
121	.probe		= spi_slave_time_probe,
122	.remove		= spi_slave_time_remove,
123};
124module_spi_driver(spi_slave_time_driver);
125
126MODULE_AUTHOR("Geert Uytterhoeven <geert+renesas@glider.be>");
127MODULE_DESCRIPTION("SPI slave reporting uptime at previous SPI message");
128MODULE_LICENSE("GPL v2");
129