> We have a design where several I2C targets with different maximum speed capability
> connected to the same I2C bus managed by one I2C master.
> We want to communicate with each target with its speed. However there is no way to
> specify the bus speed for the I2C message.

Rightfully so. Devices with a lower max_freq may get confused and block
the bus if you operate at a higher freq. You have to live with the
lowest max_freq. Or put the slow devices to another adapter. Or behind a
mux. Something like this.