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 71 struct 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 96 static 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(drvdata->irq); 104 return 0; 105 } 106 107 static void ps2_gpio_close(struct serio *serio) 108 { 109 struct ps2_gpio_data *drvdata = serio->port_data; 110 111 flush_delayed_work(&drvdata->tx.work); 112 disable_irq(drvdata->irq); 113 } 114 115 static 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(drvdata->irq); 120 gpiod_direction_output(drvdata->gpio_clk, 0); 121 122 drvdata->mode = PS2_MODE_TX; 123 drvdata->tx.byte = val; 124 125 schedule_delayed_work(&drvdata->tx.work, usecs_to_jiffies(200)); 126 127 return 0; 128 } 129 130 static 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 mutex_lock(&drvdata->tx.mutex); 137 __ps2_gpio_write(serio, val); 138 if (!wait_for_completion_timeout(&drvdata->tx.complete, 139 msecs_to_jiffies(10000))) 140 ret = SERIO_TIMEOUT; 141 mutex_unlock(&drvdata->tx.mutex); 142 } else { 143 __ps2_gpio_write(serio, val); 144 } 145 146 return ret; 147 } 148 149 static 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(drvdata->irq); 158 gpiod_direction_output(drvdata->gpio_data, 0); 159 gpiod_direction_input(drvdata->gpio_clk); 160 } 161 162 static 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(drvdata->t_irq_now, 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(drvdata->t_irq_now, 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(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(drvdata->serio, byte, 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 */ 260 261 err: 262 cnt = byte = 0; 263 __ps2_gpio_write(drvdata->serio, PS2_CMD_RESEND); 264 end: 265 drvdata->rx.cnt = cnt; 266 drvdata->rx.byte = byte; 267 return IRQ_HANDLED; 268 } 269 270 static 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(drvdata->t_irq_now, 288 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(drvdata->t_irq_now, 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(drvdata->gpio_data, data); 319 break; 320 case PS2_PARITY_BIT: 321 /* do odd parity */ 322 data = !(hweight8(byte) & 1); 323 gpiod_set_value(drvdata->gpio_data, data); 324 break; 325 case PS2_STOP_BIT: 326 /* release data line to generate stop bit */ 327 gpiod_direction_input(drvdata->gpio_data); 328 break; 329 case PS2_ACK_BIT: 330 data = gpiod_get_value(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(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 */ 354 355 err: 356 cnt = 1; 357 gpiod_direction_input(drvdata->gpio_data); 358 __ps2_gpio_write(drvdata->serio, drvdata->tx.byte); 359 end: 360 drvdata->tx.cnt = cnt; 361 return IRQ_HANDLED; 362 } 363 364 static 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 } 371 372 static 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, "data", gflags); 381 if (IS_ERR(drvdata->gpio_data)) { 382 dev_err(dev, "failed to request data gpio: %ld", 383 PTR_ERR(drvdata->gpio_data)); 384 return PTR_ERR(drvdata->gpio_data); 385 } 386 387 drvdata->gpio_clk = devm_gpiod_get(dev, "clk", gflags); 388 if (IS_ERR(drvdata->gpio_clk)) { 389 dev_err(dev, "failed to request clock gpio: %ld", 390 PTR_ERR(drvdata->gpio_clk)); 391 return PTR_ERR(drvdata->gpio_clk); 392 } 393 394 drvdata->write_enable = device_property_read_bool(dev, 395 "write-enable"); 396 397 return 0; 398 } 399 400 static 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, sizeof(struct ps2_gpio_data), GFP_KERNEL); 408 serio = kzalloc(sizeof(struct 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(drvdata->gpio_data) || 419 gpiod_cansleep(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, drvdata->irq, ps2_gpio_irq, 432 IRQF_NO_THREAD, DRIVER_NAME, drvdata); 433 if (error) { 434 dev_err(dev, "failed to request irq %d: %d\n", 435 drvdata->irq, error); 436 goto err_free_serio; 437 } 438 439 /* Keep irq disabled until serio->open is called. */ 440 disable_irq(drvdata->irq); 441 442 serio->id.type = SERIO_8042; 443 serio->open = ps2_gpio_open; 444 serio->close = ps2_gpio_close; 445 /* 446 * Write can be enabled in platform/dt data, but possibly it will not 447 * work because of the tough timings. 448 */ 449 serio->write = drvdata->write_enable ? ps2_gpio_write : NULL; 450 serio->port_data = drvdata; 451 serio->dev.parent = dev; 452 strscpy(serio->name, dev_name(dev), sizeof(serio->name)); 453 strscpy(serio->phys, dev_name(dev), sizeof(serio->phys)); 454 455 drvdata->serio = serio; 456 drvdata->dev = dev; 457 drvdata->mode = PS2_MODE_RX; 458 459 /* 460 * Tx count always starts at 1, as the start bit is sent implicitly by 461 * host-to-device communication initialization. 462 */ 463 drvdata->tx.cnt = 1; 464 465 INIT_DELAYED_WORK(&drvdata->tx.work, ps2_gpio_tx_work_fn); 466 init_completion(&drvdata->tx.complete); 467 mutex_init(&drvdata->tx.mutex); 468 469 serio_register_port(serio); 470 platform_set_drvdata(pdev, drvdata); 471 472 return 0; /* success */ 473 474 err_free_serio: 475 kfree(serio); 476 return error; 477 } 478 479 static void ps2_gpio_remove(struct platform_device *pdev) 480 { 481 struct ps2_gpio_data *drvdata = platform_get_drvdata(pdev); 482 483 serio_unregister_port(drvdata->serio); 484 } 485 486 #if defined(CONFIG_OF) 487 static const struct of_device_id ps2_gpio_match[] = { 488 { .compatible = "ps2-gpio", }, 489 { }, 490 }; 491 MODULE_DEVICE_TABLE(of, ps2_gpio_match); 492 #endif 493 494 static struct platform_driver ps2_gpio_driver = { 495 .probe = ps2_gpio_probe, 496 .remove_new = ps2_gpio_remove, 497 .driver = { 498 .name = DRIVER_NAME, 499 .of_match_table = of_match_ptr(ps2_gpio_match), 500 }, 501 }; 502 module_platform_driver(ps2_gpio_driver); 503 504 MODULE_AUTHOR("Danilo Krummrich <danilokrummrich@dk-develop.de>"); 505 MODULE_DESCRIPTION("GPIO PS2 driver"); 506 MODULE_LICENSE("GPL v2"); 507