ata: libata-sata: Add link_power_management_supported sysfs attribute

commit 0060beec0bfa647c4b510df188b1c4673a197839 upstream.

A port link power management (LPM) policy can be controlled using the
link_power_management_policy sysfs host attribute. However, this
attribute exists also for hosts that do not support LPM and in such
case, attempting to change the LPM policy for the host (port) will fail
with -EOPNOTSUPP.

Introduce the new sysfs link_power_management_supported host attribute
to indicate to the user if a the port and the devices connected to the
port for the host support LPM, which implies that the
link_power_management_policy attribute can be used.

Since checking that a port and its devices support LPM is common between
the new ata_scsi_lpm_supported_show() function and the existing
ata_scsi_lpm_store() function, the new helper ata_scsi_lpm_supported()
is introduced.

Fixes: 413e800cadbf ("ata: libata-sata: Disallow changing LPM state if not supported")
Reported-by: Borah, Chaitanya Kumar <chaitanya.kumar.borah@intel.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202507251014.a5becc3b-lkp@intel.com
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 43 insertions, 12 deletions

diff --git a/drivers/ata/ata_piix.c b/drivers/ata/ata_piix.c
index 093b940bc953..d3cda803ae06 100644
--- a/drivers/ata/ata_piix.c
+++ b/drivers/ata/ata_piix.c
@@ -1089,6 +1089,7 @@ static struct ata_port_operations ich_pata_ops = {
 };
 
 static struct attribute *piix_sidpr_shost_attrs[] = {
+	&dev_attr_link_power_management_supported.attr,
 	&dev_attr_link_power_management_policy.attr,
 	NULL
 };
diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index a28ffe1e5969..7824e8836a54 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -111,6 +111,7 @@ static DEVICE_ATTR(em_buffer, S_IWUSR | S_IRUGO,
 static DEVICE_ATTR(em_message_supported, S_IRUGO, ahci_show_em_supported, NULL);
 
 static struct attribute *ahci_shost_attrs[] = {
+	&dev_attr_link_power_management_supported.attr,
 	&dev_attr_link_power_management_policy.attr,
 	&dev_attr_em_message_type.attr,
 	&dev_attr_em_message.attr,
diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
index f1e8dbc2d564..cad3855373cb 100644
--- a/drivers/ata/libata-sata.c
+++ b/drivers/ata/libata-sata.c
@@ -900,14 +900,52 @@ static const char *ata_lpm_policy_names[] = {
 	[ATA_LPM_MIN_POWER]		= "min_power",
 };
 
+/*
+ * Check if a port supports link power management.
+ * Must be called with the port locked.
+ */
+static bool ata_scsi_lpm_supported(struct ata_port *ap)
+{
+	struct ata_link *link;
+	struct ata_device *dev;
+
+	if (ap->flags & ATA_FLAG_NO_LPM)
+		return false;
+
+	ata_for_each_link(link, ap, EDGE) {
+		ata_for_each_dev(dev, &ap->link, ENABLED) {
+			if (dev->quirks & ATA_QUIRK_NOLPM)
+				return false;
+		}
+	}
+
+	return true;
+}
+
+static ssize_t ata_scsi_lpm_supported_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct ata_port *ap = ata_shost_to_port(shost);
+	unsigned long flags;
+	bool supported;
+
+	spin_lock_irqsave(ap->lock, flags);
+	supported = ata_scsi_lpm_supported(ap);
+	spin_unlock_irqrestore(ap->lock, flags);
+
+	return sysfs_emit(buf, "%d\n", supported);
+}
+DEVICE_ATTR(link_power_management_supported, S_IRUGO,
+	    ata_scsi_lpm_supported_show, NULL);
+EXPORT_SYMBOL_GPL(dev_attr_link_power_management_supported);
+
 static ssize_t ata_scsi_lpm_store(struct device *device,
 				  struct device_attribute *attr,
 				  const char *buf, size_t count)
 {
 	struct Scsi_Host *shost = class_to_shost(device);
 	struct ata_port *ap = ata_shost_to_port(shost);
-	struct ata_link *link;
-	struct ata_device *dev;
 	enum ata_lpm_policy policy;
 	unsigned long flags;
 
@@ -924,20 +962,11 @@ static ssize_t ata_scsi_lpm_store(struct device *device,
 
 	spin_lock_irqsave(ap->lock, flags);
 
-	if (ap->flags & ATA_FLAG_NO_LPM) {
+	if (!ata_scsi_lpm_supported(ap)) {
 		count = -EOPNOTSUPP;
 		goto out_unlock;
 	}
 
-	ata_for_each_link(link, ap, EDGE) {
-		ata_for_each_dev(dev, &ap->link, ENABLED) {
-			if (dev->quirks & ATA_QUIRK_NOLPM) {
-				count = -EOPNOTSUPP;
-				goto out_unlock;
-			}
-		}
-	}
-
 	ap->target_lpm_policy = policy;
 	ata_port_schedule_eh(ap);
 out_unlock: