ata: ahci: Disallow LPM policy control if not supported

ata: ahci: Disallow LPM policy control if not supported

Commit fa997b0576c9 ("ata: ahci: Do not enable LPM if no LPM states are
supported by the HBA") introduced an early return in
ahci_update_initial_lpm_policy() to ensure that the target_lpm_policy
of ports belonging to a host that does not support the Partial, Slumber
and DevSleep power states is unchanged and remains set to
ATA_LPM_UNKNOWN and thus prevents the execution of
ata_eh_link_set_lpm().

However, a user or a system daemon (e.g. systemd-udevd) may still
attempt changing the LPM policy through the sysfs
link_power_management_policy of the host.

Improve this to prevent sysfs LPM policy changes by setting the flag
ATA_FLAG_NO_LPM for the port of such host, and initialize the port
target_lpm_policy to ATA_LPM_MAX_POWER to guarantee that no unsupported
low power state is being used on the port and its link.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://lore.kernel.org/r/20250701125321.69496-9-dlemoal@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>