i2c: designware: Add support for bus clear feature

[pelwell]

Newer versions of the DesignWare I2C block support the detection of stuck signals, and a mechanism to recover from them. Add the required software support to the driver.

This change was prompted by the observation that reading a single byte from register 0 of a VEML7700 seems to cause it to issue an ACK too early, and the controller to complain about losing arbitration. There is a suspicion that this may be a more widespread problem, but at least this patch prevents the bus from locking up.

See: #6057

[pelwell]

I can provoke the lockup using a VEML7700 by running:

$ i2cget -y 1 0x10 0; i2cget -y 1 0x10 0

Reading pairs of bytes, as expected by the device, does not exhibit the problem:

$ i2cget -y 1 0x10 0 w; i2cget -y 1 0x10 0 w

[pelwell]

It's also worth noting that the same sequence also causes an error on Pi 4 (and presumably the other members of the BCM2835 family). For anyone interested, the early ACK makes the read portion of the second access appear as another write, i.e:

SW10A00ASR10AvvNP
SW10A00ASW10NP

S=Start, W=Write, A=ACK, R=Read, N=NAK, P=Stop, vv=Variable value

[pelwell]

The autobuilds have completed - running sudo rpi-update pulls/6071 will install a trial, beta kernel including this patch. Remember to back-up important data before installing, just in case.

[JinShil]

I tested this on a number of different slave devices and did not observe any regressions.

[pelwell]

Thanks - that's good to hear.