1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 18d97d5c7d90..677c0c1b03bd 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4787,6 +4787,10 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
  *      ata_qc_new - Request an available ATA command, for queueing
  *      @ap: target port
  *
+ *      Some ATA host controllers may implement a queue depth which is less
+ *      than ATA_MAX_QUEUE. So we shouldn't allocate a tag which is beyond
+ *      the hardware limitation.
+ *
  *      LOCKING:
  *      None.
  */
@@ -4794,14 +4798,15 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
 static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
 {
         struct ata_queued_cmd *qc = NULL;
+        unsigned int max_queue = ap->host->n_tags;
         unsigned int i, tag;
 
         /* no command while frozen */
         if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
                 return NULL;
 
-        for (i = 0; i < ATA_MAX_QUEUE; i++) {
-                tag = (i + ap->last_tag + 1) % ATA_MAX_QUEUE;
+        for (i = 0, tag = ap->last_tag + 1; i < max_queue; i++, tag++) {
+                tag = tag < max_queue ? tag : 0;
 
                 /* the last tag is reserved for internal command. */
                 if (tag == ATA_TAG_INTERNAL)
@@ -6088,6 +6093,7 @@ void ata_host_init(struct ata_host *host, struct device *dev,
 {
         spin_lock_init(&host->lock);
         mutex_init(&host->eh_mutex);
+        host->n_tags = ATA_MAX_QUEUE - 1;
         host->dev = dev;
         host->ops = ops;
 }
@@ -6169,6 +6175,8 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
 {
         int i, rc;
 
+        host->n_tags = clamp(sht->can_queue, 1, ATA_MAX_QUEUE - 1);
+
         /* host must have been started */
         if (!(host->flags & ATA_HOST_STARTED)) {
                 dev_err(host->dev, "BUG: trying to register unstarted host\n");