Commit 97a23070 authored by Kevin Hao's avatar Kevin Hao Committed by Greg Kroah-Hartman

libata: support the ata host which implements a queue depth less than 32

commit 1871ee134b73fb4cadab75752a7152ed2813c751 upstream.

The sata on fsl mpc8315e is broken after the commit 8a4aeec8d2d6
("libata/ahci: accommodate tag ordered controllers"). The reason is
that the ata controller on this SoC only implement a queue depth of
16. When issuing the commands in tag order, all the commands in tag
16 ~ 31 are mapped to tag 0 unconditionally and then causes the sata
malfunction. It makes no senses to use a 32 queue in software while
the hardware has less queue depth. So consider the queue depth
implemented by the hardware when requesting a command tag.

Fixes: 8a4aeec8d2d6 ("libata/ahci: accommodate tag ordered controllers")
Signed-off-by: 's avatarKevin Hao <>
Acked-by: 's avatarDan Williams <>
Signed-off-by: 's avatarTejun Heo <>
Signed-off-by: 's avatarGreg Kroah-Hartman <>
parent cb454b6d
......@@ -4758,6 +4758,10 @@ 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.
* None.
......@@ -4765,14 +4769,16 @@ 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 i, tag;
unsigned int i, tag, max_queue;
max_queue = ap->scsi_host->can_queue;
/* 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)
......@@ -6154,6 +6160,16 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
int i, rc;
* The max queue supported by hardware must not be greater than
if (sht->can_queue > ATA_MAX_QUEUE) {
dev_err(host->dev, "BUG: the hardware max queue is too large\n");
return -EINVAL;
/* host must have been started */
if (!(host->flags & ATA_HOST_STARTED)) {
dev_err(host->dev, "BUG: trying to register unstarted host\n");
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