1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause
31  * Generic I2C bit-banging code
41  * From Linux I2C generic interface
42  * (c) 1998 Gerd Knorr <kraxel@cs.tu-berlin.de>
136 	device_set_desc(dev, "I2C bit-banging driver");  in iicbb_probe()
146 	sc->iicbus = device_add_child(dev, "iicbus", DEVICE_UNIT_ANY);  in iicbb_attach()
147 	if (!sc->iicbus)  in iicbb_attach()
150 	sc->scl_low_timeout = DEFAULT_SCL_LOW_TIMEOUT;  in iicbb_attach()
154 	    "delay", CTLFLAG_RD, &sc->udelay,  in iicbb_attach()
159 	    "scl_low_timeout", CTLFLAG_RWTUN, &sc->scl_low_timeout,  in iicbb_attach()
163 	    "io_latency", CTLFLAG_RWTUN, &sc->io_latency,  in iicbb_attach()
175 	/* We only have one child, the I2C bus, which needs our own node. */  in iicbb_get_node()
185 	if (child == sc->iicbus)  in iicbb_child_detached()
186 		sc->iicbus = NULL;  in iicbb_child_detached()
197 	/* retrieve the interface I2C address */  in iicbb_print_child()
200 		retval += printf(" on %s master-only\n",  in iicbb_print_child()
219     &i2c_debug, 0, "Enable i2c bit-banging driver debug");
243 	timeout = now + sc->scl_low_timeout * SBT_1US;  in iicbb_waitforscl()
252 		pause_sbt("iicbb-scl-low", SBT_1MS, 0, C_PREL(2));  in iicbb_waitforscl()
264 iicbb_clockin(device_t dev, int sda)  in iicbb_clockin()  argument
270 	 * - set SDA to the value;  in iicbb_clockin()
271 	 * - release SCL and wait until it's high.  in iicbb_clockin()
274 	 * There should be a data set-up time, 250 ns minimum, between setting  in iicbb_clockin()
275 	 * SDA and raising SCL.  It's expected that the I/O access latency will  in iicbb_clockin()
278 	I2C_SETSDA(dev, sda);  in iicbb_clockin()
295 	 * - pull SCL low and hold for udelay.  in iicbb_clockout()
298 	DELAY(sc->udelay);  in iicbb_clockout()
310 	DELAY(sc->udelay);  in iicbb_sendbit()
327  * line low and then the SLAVE will release the SDA (data) line.
336 	/* Release SDA so that the slave can drive it. */  in iicbb_getack()
343 	/* Sample SDA until ACK (low) or udelay runs out. */  in iicbb_getack()
350 	} while(t < sc->udelay);  in iicbb_getack()
352 	DELAY(sc->udelay - t);  in iicbb_getack()
355 	I2C_DEBUG(printf("%c ", noack ? '-' : '+'));  in iicbb_getack()
364 	for (i = 7; i >= 0; i--) {  in iicbb_sendbyte()
382 	 * Release SDA so that the slave can drive it.  in iicbb_readbyte()
383 	 * We do not use iicbb_clockin() here because we need to release SDA  in iicbb_readbyte()
388 	for (i = 7; i >= 0; i--) {  in iicbb_readbyte()
395 		DELAY((sc->udelay + 1) / 2);  in iicbb_readbyte()
398 		DELAY((sc->udelay + 1) / 2);  in iicbb_readbyte()
403 	 * Send master->slave ACK (low) for more data,  in iicbb_readbyte()
407 	I2C_DEBUG(printf("r%02x%c ", *data, last ? '-' : '+'));  in iicbb_readbyte()
444 		/* SDA will go low in the middle of the SCL high phase. */  in iicbb_start_impl()
445 		DELAY((sc->udelay + 1) / 2);  in iicbb_start_impl()
449 	 * SDA must be high after the earlier stop condition or the end  in iicbb_start_impl()
457 	/* Start: SDA high->low. */  in iicbb_start_impl()
461 	DELAY((sc->udelay + 1) / 2);  in iicbb_start_impl()
498 	 * Stop: SDA goes from low to high in the middle of the SCL high phase.  in iicbb_stop()
503 	DELAY((sc->udelay + 1) / 2);  in iicbb_stop()
505 	DELAY((sc->udelay + 1) / 2);  in iicbb_stop()
528 		len--;  in iicbb_write()
549 		len--;  in iicbb_read()
580 	busfreq = IICBUS_GET_FREQUENCY(sc->iicbus, speed);  in iicbb_set_speed()
581 	period = 1000000 / 2 / busfreq;	/* Hz -> uS */  in iicbb_set_speed()
582 	period -= sc->io_latency;  in iicbb_set_speed()
583 	sc->udelay = MAX(period, 1);  in iicbb_set_speed()