1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * pps_parport.c -- kernel parallel port PPS client
4 *
5 * Copyright (C) 2009   Alexander Gordeev <lasaine@lvk.cs.msu.su>
6 */
7
8
9/*
10 * TODO:
11 * implement echo over SEL pin
12 */
13
14#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15
16#include <linux/kernel.h>
17#include <linux/module.h>
18#include <linux/init.h>
19#include <linux/irqnr.h>
20#include <linux/time.h>
21#include <linux/slab.h>
22#include <linux/parport.h>
23#include <linux/pps_kernel.h>
24
25/* module parameters */
26
27#define CLEAR_WAIT_MAX		100
28#define CLEAR_WAIT_MAX_ERRORS	5
29
30static unsigned int clear_wait = 100;
31MODULE_PARM_DESC(clear_wait,
32	"Maximum number of port reads when polling for signal clear,"
33	" zero turns clear edge capture off entirely");
34module_param(clear_wait, uint, 0);
35
36static DEFINE_IDA(pps_client_index);
37
38/* internal per port structure */
39struct pps_client_pp {
40	struct pardevice *pardev;	/* parport device */
41	struct pps_device *pps;		/* PPS device */
42	unsigned int cw;		/* port clear timeout */
43	unsigned int cw_err;		/* number of timeouts */
44	int index;			/* device number */
45};
46
47static inline int signal_is_set(struct parport *port)
48{
49	return (port->ops->read_status(port) & PARPORT_STATUS_ACK) != 0;
50}
51
52/* parport interrupt handler */
53static void parport_irq(void *handle)
54{
55	struct pps_event_time ts_assert, ts_clear;
56	struct pps_client_pp *dev = handle;
57	struct parport *port = dev->pardev->port;
58	unsigned int i;
59	unsigned long flags;
60
61	/* first of all we get the time stamp... */
62	pps_get_ts(&ts_assert);
63
64	if (dev->cw == 0)
65		/* clear edge capture disabled */
66		goto out_assert;
67
68	/* try capture the clear edge */
69
70	/* We have to disable interrupts here. The idea is to prevent
71	 * other interrupts on the same processor to introduce random
72	 * lags while polling the port. Reading from IO port is known
73	 * to take approximately 1us while other interrupt handlers can
74	 * take much more potentially.
75	 *
76	 * Interrupts won't be disabled for a long time because the
77	 * number of polls is limited by clear_wait parameter which is
78	 * kept rather low. So it should never be an issue.
79	 */
80	local_irq_save(flags);
81	/* check the signal (no signal means the pulse is lost this time) */
82	if (!signal_is_set(port)) {
83		local_irq_restore(flags);
84		dev_err(dev->pps->dev, "lost the signal\n");
85		goto out_assert;
86	}
87
88	/* poll the port until the signal is unset */
89	for (i = dev->cw; i; i--)
90		if (!signal_is_set(port)) {
91			pps_get_ts(&ts_clear);
92			local_irq_restore(flags);
93			dev->cw_err = 0;
94			goto out_both;
95		}
96	local_irq_restore(flags);
97
98	/* timeout */
99	dev->cw_err++;
100	if (dev->cw_err >= CLEAR_WAIT_MAX_ERRORS) {
101		dev_err(dev->pps->dev, "disabled clear edge capture after %d"
102				" timeouts\n", dev->cw_err);
103		dev->cw = 0;
104		dev->cw_err = 0;
105	}
106
107out_assert:
108	/* fire assert event */
109	pps_event(dev->pps, &ts_assert,
110			PPS_CAPTUREASSERT, NULL);
111	return;
112
113out_both:
114	/* fire assert event */
115	pps_event(dev->pps, &ts_assert,
116			PPS_CAPTUREASSERT, NULL);
117	/* fire clear event */
118	pps_event(dev->pps, &ts_clear,
119			PPS_CAPTURECLEAR, NULL);
120	return;
121}
122
123static void parport_attach(struct parport *port)
124{
125	struct pardev_cb pps_client_cb;
126	int index;
127	struct pps_client_pp *device;
128	struct pps_source_info info = {
129		.name		= KBUILD_MODNAME,
130		.path		= "",
131		.mode		= PPS_CAPTUREBOTH | \
132				  PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
133				  PPS_ECHOASSERT | PPS_ECHOCLEAR | \
134				  PPS_CANWAIT | PPS_TSFMT_TSPEC,
135		.owner		= THIS_MODULE,
136		.dev		= NULL
137	};
138
139	if (clear_wait > CLEAR_WAIT_MAX) {
140		pr_err("clear_wait value should be not greater then %d\n",
141		       CLEAR_WAIT_MAX);
142		return;
143	}
144
145	device = kzalloc(sizeof(struct pps_client_pp), GFP_KERNEL);
146	if (!device) {
147		pr_err("memory allocation failed, not attaching\n");
148		return;
149	}
150
151	index = ida_simple_get(&pps_client_index, 0, 0, GFP_KERNEL);
152	memset(&pps_client_cb, 0, sizeof(pps_client_cb));
153	pps_client_cb.private = device;
154	pps_client_cb.irq_func = parport_irq;
155	pps_client_cb.flags = PARPORT_FLAG_EXCL;
156	device->pardev = parport_register_dev_model(port,
157						    KBUILD_MODNAME,
158						    &pps_client_cb,
159						    index);
160	if (!device->pardev) {
161		pr_err("couldn't register with %s\n", port->name);
162		goto err_free;
163	}
164
165	if (parport_claim_or_block(device->pardev) < 0) {
166		pr_err("couldn't claim %s\n", port->name);
167		goto err_unregister_dev;
168	}
169
170	device->pps = pps_register_source(&info,
171			PPS_CAPTUREBOTH | PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
172	if (IS_ERR(device->pps)) {
173		pr_err("couldn't register PPS source\n");
174		goto err_release_dev;
175	}
176
177	device->cw = clear_wait;
178
179	port->ops->enable_irq(port);
180	device->index = index;
181
182	pr_info("attached to %s\n", port->name);
183
184	return;
185
186err_release_dev:
187	parport_release(device->pardev);
188err_unregister_dev:
189	parport_unregister_device(device->pardev);
190err_free:
191	ida_simple_remove(&pps_client_index, index);
192	kfree(device);
193}
194
195static void parport_detach(struct parport *port)
196{
197	struct pardevice *pardev = port->cad;
198	struct pps_client_pp *device;
199
200	/* FIXME: oooh, this is ugly! */
201	if (!pardev || strcmp(pardev->name, KBUILD_MODNAME))
202		/* not our port */
203		return;
204
205	device = pardev->private;
206
207	port->ops->disable_irq(port);
208	pps_unregister_source(device->pps);
209	parport_release(pardev);
210	parport_unregister_device(pardev);
211	ida_simple_remove(&pps_client_index, device->index);
212	kfree(device);
213}
214
215static struct parport_driver pps_parport_driver = {
216	.name = KBUILD_MODNAME,
217	.match_port = parport_attach,
218	.detach = parport_detach,
219	.devmodel = true,
220};
221module_parport_driver(pps_parport_driver);
222
223MODULE_AUTHOR("Alexander Gordeev <lasaine@lvk.cs.msu.su>");
224MODULE_DESCRIPTION("parallel port PPS client");
225MODULE_LICENSE("GPL");
226