1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * GPIO based serio bus driver for bit banging the PS/2 protocol
4 *
5 * Author: Danilo Krummrich <danilokrummrich@dk-develop.de>
6 */
7
8#include <linux/gpio/consumer.h>
9#include <linux/interrupt.h>
10#include <linux/module.h>
11#include <linux/serio.h>
12#include <linux/slab.h>
13#include <linux/platform_device.h>
14#include <linux/workqueue.h>
15#include <linux/completion.h>
16#include <linux/mutex.h>
17#include <linux/preempt.h>
18#include <linux/property.h>
19#include <linux/of.h>
20#include <linux/jiffies.h>
21#include <linux/delay.h>
22#include <linux/timekeeping.h>
23
24#define DRIVER_NAME "ps2-gpio"
25
26#define PS2_MODE_RX 0
27#define PS2_MODE_TX 1
28
29#define PS2_START_BIT 0
30#define PS2_DATA_BIT0 1
31#define PS2_DATA_BIT1 2
32#define PS2_DATA_BIT2 3
33#define PS2_DATA_BIT3 4
34#define PS2_DATA_BIT4 5
35#define PS2_DATA_BIT5 6
36#define PS2_DATA_BIT6 7
37#define PS2_DATA_BIT7 8
38#define PS2_PARITY_BIT 9
39#define PS2_STOP_BIT 10
40#define PS2_ACK_BIT 11
41
42#define PS2_DEV_RET_ACK 0xfa
43#define PS2_DEV_RET_NACK 0xfe
44
45#define PS2_CMD_RESEND 0xfe
46
47/*
48 * The PS2 protocol specifies a clock frequency between 10kHz and 16.7kHz,
49 * therefore the maximal interrupt interval should be 100us and the minimum
50 * interrupt interval should be ~60us. Let's allow +/- 20us for frequency
51 * deviations and interrupt latency.
52 *
53 * The data line must be samples after ~30us to 50us after the falling edge,
54 * since the device updates the data line at the rising edge.
55 *
56 * ___ ______ ______ ______ ___
57 * \ / \ / \ / \ /
58 * \ / \ / \ / \ /
59 * \______/ \______/ \______/ \______/
60 *
61 * |-----------------| |--------|
62 * 60us/100us 30us/50us
63 */
64#define PS2_CLK_FREQ_MIN_HZ 10000
65#define PS2_CLK_FREQ_MAX_HZ 16700
66#define PS2_CLK_MIN_INTERVAL_US ((1000 * 1000) / PS2_CLK_FREQ_MAX_HZ)
67#define PS2_CLK_MAX_INTERVAL_US ((1000 * 1000) / PS2_CLK_FREQ_MIN_HZ)
68#define PS2_IRQ_MIN_INTERVAL_US (PS2_CLK_MIN_INTERVAL_US - 20)
69#define PS2_IRQ_MAX_INTERVAL_US (PS2_CLK_MAX_INTERVAL_US + 20)
70
71struct ps2_gpio_data {
72 struct device *dev;
73 struct serio *serio;
74 unsigned char mode;
75 struct gpio_desc *gpio_clk;
76 struct gpio_desc *gpio_data;
77 bool write_enable;
78 int irq;
79 ktime_t t_irq_now;
80 ktime_t t_irq_last;
81 struct {
82 unsigned char cnt;
83 unsigned char byte;
84 } rx;
85 struct {
86 unsigned char cnt;
87 unsigned char byte;
88 ktime_t t_xfer_start;
89 ktime_t t_xfer_end;
90 struct completion complete;
91 struct mutex mutex;
92 struct delayed_work work;
93 } tx;
94};
95
96static int ps2_gpio_open(struct serio *serio)
97{
98 struct ps2_gpio_data *drvdata = serio->port_data;
99
100 drvdata->t_irq_last = 0;
101 drvdata->tx.t_xfer_end = 0;
102
103 enable_irq(irq: drvdata->irq);
104 return 0;
105}
106
107static void ps2_gpio_close(struct serio *serio)
108{
109 struct ps2_gpio_data *drvdata = serio->port_data;
110
111 flush_delayed_work(dwork: &drvdata->tx.work);
112 disable_irq(irq: drvdata->irq);
113}
114
115static int __ps2_gpio_write(struct serio *serio, unsigned char val)
116{
117 struct ps2_gpio_data *drvdata = serio->port_data;
118
119 disable_irq_nosync(irq: drvdata->irq);
120 gpiod_direction_output(desc: drvdata->gpio_clk, value: 0);
121
122 drvdata->mode = PS2_MODE_TX;
123 drvdata->tx.byte = val;
124
125 schedule_delayed_work(dwork: &drvdata->tx.work, delay: usecs_to_jiffies(u: 200));
126
127 return 0;
128}
129
130static int ps2_gpio_write(struct serio *serio, unsigned char val)
131{
132 struct ps2_gpio_data *drvdata = serio->port_data;
133 int ret = 0;
134
135 if (in_task()) {
136 guard(mutex)(T: &drvdata->tx.mutex);
137
138 __ps2_gpio_write(serio, val);
139 if (!wait_for_completion_timeout(x: &drvdata->tx.complete,
140 timeout: msecs_to_jiffies(m: 10000)))
141 ret = SERIO_TIMEOUT;
142 } else {
143 __ps2_gpio_write(serio, val);
144 }
145
146 return ret;
147}
148
149static void ps2_gpio_tx_work_fn(struct work_struct *work)
150{
151 struct delayed_work *dwork = to_delayed_work(work);
152 struct ps2_gpio_data *drvdata = container_of(dwork,
153 struct ps2_gpio_data,
154 tx.work);
155
156 drvdata->tx.t_xfer_start = ktime_get();
157 enable_irq(irq: drvdata->irq);
158 gpiod_direction_output(desc: drvdata->gpio_data, value: 0);
159 gpiod_direction_input(desc: drvdata->gpio_clk);
160}
161
162static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata)
163{
164 unsigned char byte, cnt;
165 int data;
166 int rxflags = 0;
167 s64 us_delta;
168
169 byte = drvdata->rx.byte;
170 cnt = drvdata->rx.cnt;
171
172 drvdata->t_irq_now = ktime_get();
173
174 /*
175 * We need to consider spurious interrupts happening right after
176 * a TX xfer finished.
177 */
178 us_delta = ktime_us_delta(later: drvdata->t_irq_now, earlier: drvdata->tx.t_xfer_end);
179 if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US))
180 goto end;
181
182 us_delta = ktime_us_delta(later: drvdata->t_irq_now, earlier: drvdata->t_irq_last);
183 if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt) {
184 dev_err(drvdata->dev,
185 "RX: timeout, probably we missed an interrupt\n");
186 goto err;
187 } else if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US)) {
188 /* Ignore spurious IRQs. */
189 goto end;
190 }
191 drvdata->t_irq_last = drvdata->t_irq_now;
192
193 data = gpiod_get_value(desc: drvdata->gpio_data);
194 if (unlikely(data < 0)) {
195 dev_err(drvdata->dev, "RX: failed to get data gpio val: %d\n",
196 data);
197 goto err;
198 }
199
200 switch (cnt) {
201 case PS2_START_BIT:
202 /* start bit should be low */
203 if (unlikely(data)) {
204 dev_err(drvdata->dev, "RX: start bit should be low\n");
205 goto err;
206 }
207 break;
208 case PS2_DATA_BIT0:
209 case PS2_DATA_BIT1:
210 case PS2_DATA_BIT2:
211 case PS2_DATA_BIT3:
212 case PS2_DATA_BIT4:
213 case PS2_DATA_BIT5:
214 case PS2_DATA_BIT6:
215 case PS2_DATA_BIT7:
216 /* processing data bits */
217 if (data)
218 byte |= (data << (cnt - 1));
219 break;
220 case PS2_PARITY_BIT:
221 /* check odd parity */
222 if (!((hweight8(byte) & 1) ^ data)) {
223 rxflags |= SERIO_PARITY;
224 dev_warn(drvdata->dev, "RX: parity error\n");
225 if (!drvdata->write_enable)
226 goto err;
227 }
228 break;
229 case PS2_STOP_BIT:
230 /* stop bit should be high */
231 if (unlikely(!data)) {
232 dev_err(drvdata->dev, "RX: stop bit should be high\n");
233 goto err;
234 }
235
236 /*
237 * Do not send spurious ACK's and NACK's when write fn is
238 * not provided.
239 */
240 if (!drvdata->write_enable) {
241 if (byte == PS2_DEV_RET_NACK)
242 goto err;
243 else if (byte == PS2_DEV_RET_ACK)
244 break;
245 }
246
247 serio_interrupt(serio: drvdata->serio, data: byte, flags: rxflags);
248 dev_dbg(drvdata->dev, "RX: sending byte 0x%x\n", byte);
249
250 cnt = byte = 0;
251
252 goto end; /* success */
253 default:
254 dev_err(drvdata->dev, "RX: got out of sync with the device\n");
255 goto err;
256 }
257
258 cnt++;
259 goto end; /* success */
260
261err:
262 cnt = byte = 0;
263 __ps2_gpio_write(serio: drvdata->serio, PS2_CMD_RESEND);
264end:
265 drvdata->rx.cnt = cnt;
266 drvdata->rx.byte = byte;
267 return IRQ_HANDLED;
268}
269
270static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata)
271{
272 unsigned char byte, cnt;
273 int data;
274 s64 us_delta;
275
276 cnt = drvdata->tx.cnt;
277 byte = drvdata->tx.byte;
278
279 drvdata->t_irq_now = ktime_get();
280
281 /*
282 * There might be pending IRQs since we disabled IRQs in
283 * __ps2_gpio_write(). We can expect at least one clock period until
284 * the device generates the first falling edge after releasing the
285 * clock line.
286 */
287 us_delta = ktime_us_delta(later: drvdata->t_irq_now,
288 earlier: drvdata->tx.t_xfer_start);
289 if (unlikely(us_delta < PS2_CLK_MIN_INTERVAL_US))
290 goto end;
291
292 us_delta = ktime_us_delta(later: drvdata->t_irq_now, earlier: drvdata->t_irq_last);
293 if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt > 1) {
294 dev_err(drvdata->dev,
295 "TX: timeout, probably we missed an interrupt\n");
296 goto err;
297 } else if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US)) {
298 /* Ignore spurious IRQs. */
299 goto end;
300 }
301 drvdata->t_irq_last = drvdata->t_irq_now;
302
303 switch (cnt) {
304 case PS2_START_BIT:
305 /* should never happen */
306 dev_err(drvdata->dev,
307 "TX: start bit should have been sent already\n");
308 goto err;
309 case PS2_DATA_BIT0:
310 case PS2_DATA_BIT1:
311 case PS2_DATA_BIT2:
312 case PS2_DATA_BIT3:
313 case PS2_DATA_BIT4:
314 case PS2_DATA_BIT5:
315 case PS2_DATA_BIT6:
316 case PS2_DATA_BIT7:
317 data = byte & BIT(cnt - 1);
318 gpiod_set_value(desc: drvdata->gpio_data, value: data);
319 break;
320 case PS2_PARITY_BIT:
321 /* do odd parity */
322 data = !(hweight8(byte) & 1);
323 gpiod_set_value(desc: drvdata->gpio_data, value: data);
324 break;
325 case PS2_STOP_BIT:
326 /* release data line to generate stop bit */
327 gpiod_direction_input(desc: drvdata->gpio_data);
328 break;
329 case PS2_ACK_BIT:
330 data = gpiod_get_value(desc: drvdata->gpio_data);
331 if (data) {
332 dev_warn(drvdata->dev, "TX: received NACK, retry\n");
333 goto err;
334 }
335
336 drvdata->tx.t_xfer_end = ktime_get();
337 drvdata->mode = PS2_MODE_RX;
338 complete(&drvdata->tx.complete);
339
340 cnt = 1;
341 goto end; /* success */
342 default:
343 /*
344 * Probably we missed the stop bit. Therefore we release data
345 * line and try again.
346 */
347 gpiod_direction_input(desc: drvdata->gpio_data);
348 dev_err(drvdata->dev, "TX: got out of sync with the device\n");
349 goto err;
350 }
351
352 cnt++;
353 goto end; /* success */
354
355err:
356 cnt = 1;
357 gpiod_direction_input(desc: drvdata->gpio_data);
358 __ps2_gpio_write(serio: drvdata->serio, val: drvdata->tx.byte);
359end:
360 drvdata->tx.cnt = cnt;
361 return IRQ_HANDLED;
362}
363
364static irqreturn_t ps2_gpio_irq(int irq, void *dev_id)
365{
366 struct ps2_gpio_data *drvdata = dev_id;
367
368 return drvdata->mode ? ps2_gpio_irq_tx(drvdata) :
369 ps2_gpio_irq_rx(drvdata);
370}
371
372static int ps2_gpio_get_props(struct device *dev,
373 struct ps2_gpio_data *drvdata)
374{
375 enum gpiod_flags gflags;
376
377 /* Enforce open drain, since this is required by the PS/2 bus. */
378 gflags = GPIOD_IN | GPIOD_FLAGS_BIT_OPEN_DRAIN;
379
380 drvdata->gpio_data = devm_gpiod_get(dev, con_id: "data", flags: gflags);
381 if (IS_ERR(ptr: drvdata->gpio_data)) {
382 dev_err(dev, "failed to request data gpio: %ld",
383 PTR_ERR(drvdata->gpio_data));
384 return PTR_ERR(ptr: drvdata->gpio_data);
385 }
386
387 drvdata->gpio_clk = devm_gpiod_get(dev, con_id: "clk", flags: gflags);
388 if (IS_ERR(ptr: drvdata->gpio_clk)) {
389 dev_err(dev, "failed to request clock gpio: %ld",
390 PTR_ERR(drvdata->gpio_clk));
391 return PTR_ERR(ptr: drvdata->gpio_clk);
392 }
393
394 drvdata->write_enable = device_property_read_bool(dev,
395 propname: "write-enable");
396
397 return 0;
398}
399
400static int ps2_gpio_probe(struct platform_device *pdev)
401{
402 struct ps2_gpio_data *drvdata;
403 struct serio *serio;
404 struct device *dev = &pdev->dev;
405 int error;
406
407 drvdata = devm_kzalloc(dev, size: sizeof(*drvdata), GFP_KERNEL);
408 serio = kzalloc(sizeof(*serio), GFP_KERNEL);
409 if (!drvdata || !serio) {
410 error = -ENOMEM;
411 goto err_free_serio;
412 }
413
414 error = ps2_gpio_get_props(dev, drvdata);
415 if (error)
416 goto err_free_serio;
417
418 if (gpiod_cansleep(desc: drvdata->gpio_data) ||
419 gpiod_cansleep(desc: drvdata->gpio_clk)) {
420 dev_err(dev, "GPIO data or clk are connected via slow bus\n");
421 error = -EINVAL;
422 goto err_free_serio;
423 }
424
425 drvdata->irq = platform_get_irq(pdev, 0);
426 if (drvdata->irq < 0) {
427 error = drvdata->irq;
428 goto err_free_serio;
429 }
430
431 error = devm_request_irq(dev, irq: drvdata->irq, handler: ps2_gpio_irq,
432 IRQF_NO_THREAD | IRQF_NO_AUTOEN, DRIVER_NAME,
433 dev_id: drvdata);
434 if (error) {
435 dev_err(dev, "failed to request irq %d: %d\n",
436 drvdata->irq, error);
437 goto err_free_serio;
438 }
439
440 serio->id.type = SERIO_8042;
441 serio->open = ps2_gpio_open;
442 serio->close = ps2_gpio_close;
443 /*
444 * Write can be enabled in platform/dt data, but possibly it will not
445 * work because of the tough timings.
446 */
447 serio->write = drvdata->write_enable ? ps2_gpio_write : NULL;
448 serio->port_data = drvdata;
449 serio->dev.parent = dev;
450 strscpy(serio->name, dev_name(dev), sizeof(serio->name));
451 strscpy(serio->phys, dev_name(dev), sizeof(serio->phys));
452
453 drvdata->serio = serio;
454 drvdata->dev = dev;
455 drvdata->mode = PS2_MODE_RX;
456
457 /*
458 * Tx count always starts at 1, as the start bit is sent implicitly by
459 * host-to-device communication initialization.
460 */
461 drvdata->tx.cnt = 1;
462
463 INIT_DELAYED_WORK(&drvdata->tx.work, ps2_gpio_tx_work_fn);
464 init_completion(x: &drvdata->tx.complete);
465 mutex_init(&drvdata->tx.mutex);
466
467 serio_register_port(serio);
468 platform_set_drvdata(pdev, data: drvdata);
469
470 return 0; /* success */
471
472err_free_serio:
473 kfree(objp: serio);
474 return error;
475}
476
477static void ps2_gpio_remove(struct platform_device *pdev)
478{
479 struct ps2_gpio_data *drvdata = platform_get_drvdata(pdev);
480
481 serio_unregister_port(serio: drvdata->serio);
482}
483
484#if defined(CONFIG_OF)
485static const struct of_device_id ps2_gpio_match[] = {
486 { .compatible = "ps2-gpio", },
487 { },
488};
489MODULE_DEVICE_TABLE(of, ps2_gpio_match);
490#endif
491
492static struct platform_driver ps2_gpio_driver = {
493 .probe = ps2_gpio_probe,
494 .remove = ps2_gpio_remove,
495 .driver = {
496 .name = DRIVER_NAME,
497 .of_match_table = of_match_ptr(ps2_gpio_match),
498 },
499};
500module_platform_driver(ps2_gpio_driver);
501
502MODULE_AUTHOR("Danilo Krummrich <danilokrummrich@dk-develop.de>");
503MODULE_DESCRIPTION("GPIO PS2 driver");
504MODULE_LICENSE("GPL v2");
505

source code of linux/drivers/input/serio/ps2-gpio.c