1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause
23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32  * Helper code to recover a hung i2c bus by bit-banging a recovery sequence.
34  * An i2c bus can be hung by a slave driving the clock (rare) or data lines low.
35  * The most common cause is a partially-completed transaction such as rebooting
36  * while a slave is sending a byte of data.  Because i2c allows the clock to
38  * data line until power is removed, or the clock cycles enough times to
42  * Any i2c driver which is able to manually set the level of the clock and data
44  * embedded i2c controllers, the i2c pins can be temporarily reassigned as gpio
45  * pins to do the bus recovery, then can be assigned back to the i2c hardware.
58 iic_recover_bus(struct iicrb_pin_access *pins)  in iic_recover_bus()  argument
65 	 * Start with clock and data high.  in iic_recover_bus()
67 	pins->setsda(pins->ctx, 1);  in iic_recover_bus()
68 	pins->setscl(pins->ctx, 1);  in iic_recover_bus()
72 	 * bus is doing clock-stretching and we should wait a while.  If that  in iic_recover_bus()
75 	 * cheap eeprom has a max post-write delay of only 10ms), and also long  in iic_recover_bus()
79 		if (pins->getscl(pins->ctx))  in iic_recover_bus()
89 	 * the data line low waiting for more clock pulses to finish the byte.  in iic_recover_bus()
90 	 * Cycle the clock until we see the data line go high, but only up to 9  in iic_recover_bus()
93 	 * bit, after which the slave must not be driving the data line anymore.  in iic_recover_bus()
96 		if (pins->getsda(pins->ctx))  in iic_recover_bus()
100 		pins->setscl(pins->ctx, 0);  in iic_recover_bus()
102 		pins->setscl(pins->ctx, 1);  in iic_recover_bus()
107 	 * At this point we should be in control of both the clock and data  in iic_recover_bus()
111 	 *  - START: SDA transitions high->low while SCL remains high.  in iic_recover_bus()
112 	 *  - STOP:  SDA transitions low->high while SCL remains high.  in iic_recover_bus()
114 	 * data line no faster than it would change state with a 100khz clock.  in iic_recover_bus()
116 	pins->setsda(pins->ctx, 0);  in iic_recover_bus()
118 	pins->setsda(pins->ctx, 1);  in iic_recover_bus()