tps6598x_powerup failed for /arm-io/i2c0/hpmBusManager/hpm1

(Split off from AsahiLinux/m1n1#97)

On my MacBook Pro, which has run other kernels and boot loaders but is currently loading vanilla m1n1, commit c2c6da3, directly from iBoot, I occasionally see messages like:

TTY> i2c: want to read 1 bytes from addr 63 but can only read 0
TTY> usb: tps6598x_powerup failed for /arm-io/i2c0/hpmBusManager/hpm1.
TTY> usb: failed to init hpm1

I’ve been unable to reproduce this at will. I’ve never seen the problem except when the power supply was connected to either one of the USB-C ports. However, it’s always hpm1 that’s mentioned in the error message.

In AsahiLinux/m1n1#72, @jannau mentions he had to add delays to the i2c code in order to avoid similar-sounding issues. Do you want me to try doing that?

[marcan]

Repro’d fairly reliably with the AV adapter.

[alyssarosenzweig]

I just did 25 boots, long-pressing the power-button between each, and got 6 failures. In four of the failure cases, no ttyACM* interface showed up; in the other two, it did, and five subsequent chainloads were successful.

My gut says “race condition”.