STM32F303 I2C `blocking_read_write` works but async `write_read` fails due to a timeout about embassy

[fmckeogh]

@jamesmunns Yes, seems like you're right. The contents of the poll_fn gets called once, returns pending, then is never called again. I've tried manually re-enabling interrupts but no luck so far, I think I need to take some time to understand the codebase.

[jamesmunns]

@fmckeogh I looked and the F303 doesn't have the errata from #2887, I would suggest adding logs to the poll_fns in the read/write dma internal to figure out which branch was taken, I'm guessing in the hanging case, it's taking one of the branches that DOESN'T re-enable the interrupts.

Since the interrupts self-disable, any non-terminating branch of the poll-fns should re-enable the interrupts.

[fmckeogh]

@jamesmunns Awesome, will do:)