The following shows up in the kernel log on systems using the STM32MP15xx USBPHYC:
"
regulator regulator.19: regulator disable timed out!
reg18: failed to disable: -ETIMEDOUT
"
This 'regulator.19' is 'pwr@50001000' 'reg18' in stm32mp151.dts DT, or
"Power control (PWR)" register "PWR_CR3" bits "REG18" on STM32MP15xx
reference manual.

The reason for the timeout seems to be the poll which this patch changes.
When turning this regulator OFF, PWR_CR3 reads 0xf0000000 , then REG18_EN
bit is cleared, and then this poll waits until REG18_RDY bit is cleared as
well, but that never happens, the PWR_CR3 keeps reading 0xe0000000 .

I am not sure whether this should happen, I suspect the 1V8 supply is
always READY when the 1V8 input is present, and the regulator can only
ever be enabled/disabled using the REG18_EN bit, but the REG18_READY
bit is never cleared again.

This patch adjusts the poll to check whether REG18_EN has been cleared
on regulator disable, but retains the check for REG18_READY in regulator
enable as there it makes sense to verify the regulator is really READY.
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20230518023946.530381-1-marex@denx.deSigned-off-by: Mark Brown <broonie@kernel.org>