[PATCH v2 2/2] ata: ahci: Protect users from setting policies their drives don't support

[Mario Limonciello]

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 policies
dependent upon slumber (`min_power` or `min_power_with_partial`) affect the
disk.

Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
Changes from v1->v2:
* Move deeper into codepaths
* Reset to MED_POWER rather than ignore
 drivers/ata/libata-sata.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
index 071158c0c44c..0dc03888c62b 100644
--- a/drivers/ata/libata-sata.c
+++ b/drivers/ata/libata-sata.c
@@ -13,6 +13,7 @@
 #include <scsi/scsi_device.h>
 #include <linux/libata.h>
 
+#include "ahci.h"
 #include "libata.h"
 #include "libata-transport.h"
 
@@ -368,10 +369,20 @@ int sata_link_scr_lpm(struct ata_link *link, enum ata_lpm_policy policy,
 		      bool spm_wakeup)
 {
 	struct ata_eh_context *ehc = &link->eh_context;
+	struct ata_port *ap = link->ap;
+	struct ahci_host_priv *hpriv;
 	bool woken_up = false;
 	u32 scontrol;
 	int rc;
 
+	hpriv = ap->host->private_data;
+	if (policy >= ATA_LPM_MIN_POWER_WITH_PARTIAL &&
+	  !(hpriv->cap & HOST_CAP_SSC)) {
+		dev_warn(ap->host->dev,
+			"This drive doesn't support slumber; restting policy to MED_POWER\n");
+		policy = ATA_LPM_MED_POWER;
+	}
+
 	rc = sata_scr_read(link, SCR_CONTROL, &scontrol);
 	if (rc)
 		return rc;
-- 
2.34.1