[RFC 2/2] ata: ahci: Protect users from setting policies their drives don't support

[Mario Limonciello <mario.limonciello@amd.com>]

As the default low power policy applies to more chipsets and drives, it's
important to make sure that drives actually support the policy that a user
selected in their kernel configuration.

If the drive doesn't support slumber, don't let the default policy for the
ATA port be `min_power` or `min_power_with_partial`.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/ata/ahci.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 17d757ad7111..af8999453084 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -1584,8 +1584,16 @@ static int ahci_init_msi(struct pci_dev *pdev, unsigned int n_ports,
 static void ahci_update_initial_lpm_policy(struct ata_port *ap,
 					   struct ahci_host_priv *hpriv)
 {
+	struct pci_dev *pdev = to_pci_dev(ap->host->dev);
 	int policy = CONFIG_SATA_LPM_POLICY;
 
+	if (policy >= ATA_LPM_MIN_POWER_WITH_PARTIAL &&
+	   !(hpriv->cap & HOST_CAP_SSC)) {
+		dev_warn(&pdev->dev,
+			 "This drive doesn't support slumber; ignoring default SATA policy\n");
+		return;
+	}
+
 	/* user modified policy via module param */
 	if (mobile_lpm_policy != -1) {
 		policy = mobile_lpm_policy;
-- 
2.34.1