Query on kernel parameter to set sata ata link speed

[SIMON BABY]

Hi,

 I am new to this group.
 I have a couple of queries regarding the setting of  SATA ATA  link speed
in the linux kernel driver.

1. Do we have any configuration in u-boot to enable reading and writing of
the SCR register associated with the ata link?
2. Currently I am not able to read the speed or any other parameters since
the reading or writing of the SCR register is not supported. Is it
something u-boot does ?
3. Can I pass a boot argument command "libata.force=1.5Gbps" in u-boot
prompt as one of the boot arguments?

Thank you for helping.
Regards
Simon