In general, 25G can operate on either PLLF or PLLS but 10G can operate on PLLS only. So if PLL usage allows it, it should be possible to switch from 25G to 10G without rebooting by starting with a known SerDes protocol and reconfiguring the desired lane(s), as we have done in other devices.
If PLLS is either not used or already configured for 10G, then the port can switch from PLLF to PLLS when switching from 25G to 10G. For example, if starting with SerDes 1 protocol 0x18 or 0x19, then sw can reconfigure one or both 25G ports to 10G ports on PLLS. If PLLF is only being used for one 25G, or if all 25G ports are switching to 10G ports at the same time, then the switch is possible. You could start with SerDes 1 0x17, 0x19, or 0x21 and switch all the 25G ports to 10G ports at the same time.
No the speed switching is not automatic. Lane reconfiguration is done in software or via PBI by changing SerDes registers with the desired Rx/Tx settings, PLL configuration, etc.
