[PATCH 08/10] ata: ahci: Disallow LPM policy control if not supported

[Damien Le Moal <dlemoal@kernel.org>]

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_FLOAG_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>
---
 drivers/ata/ahci.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 34698ae39f55..737f5d1bde11 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -1793,7 +1793,10 @@ static void ahci_update_initial_lpm_policy(struct ata_port *ap)
 	if ((ap->host->flags & ATA_HOST_NO_PART) &&
 	    (ap->host->flags & ATA_HOST_NO_SSC) &&
 	    (ap->host->flags & ATA_HOST_NO_DEVSLP)) {
-		ata_port_dbg(ap, "no LPM states supported, not enabling LPM\n");
+		ata_port_warn(ap,
+			"No LPM states supported, forcing LPM max_power\n");
+		ap->flags |= ATA_FLAG_NO_LPM;
+		ap->target_lpm_policy = ATA_LPM_MAX_POWER;
 		return;
 	}
 
-- 
2.50.0