On Tue, Sep 21, 2021 at 08:37:28AM +0200, Peter Rosin wrote:

> I expected it to just work to mark the register as readable and do
> without the default value (i.e. the way it was before my patch). What
> I don't understand is why regmap returns -EBUSY in that case. That
> doesn't make sense to me. Perhaps that -EBUSY is propagated from the
> I2C layer, but in that case, why is it then ok to do a write to
> another register at the same spot in the code? So, why -EBUSY?

Actually one thing that can trigger this now I think about it is
attempting to access a volatile register when the device is in cache
only mode for power management reasons - if the device is in cache only
mode then you can't do a hardware read so volatile registers become
inaccessible.