Re: [PATCH RFC 2/2] libata: Use scsi cmnd budget token for qc tag for SAS host

Christoph Hellwig
2022-03-16T08:34:50Z

In addition to the comments from Damien: I think we should kill
ata_qc_new_init as well. It is a bit pointless and having it in
libata-core.c when it pokes into scsi internals also doesn't make sense.

So maybe something like:

diff --git a/Documentation/driver-api/libata.rst b/Documentation/driver-api/libata.rst
index d477e296bda5f2..311af516a3fd9c 100644
--- a/Documentation/driver-api/libata.rst
+++ b/Documentation/driver-api/libata.rst
@@ -424,12 +424,6 @@ How commands are issued
-----------------------

Internal commands
- First, qc is allocated and initialized using :c:func:`ata_qc_new_init`.
- Although :c:func:`ata_qc_new_init` doesn't implement any wait or retry
- mechanism when qc is not available, internal commands are currently
- issued only during initialization and error recovery, so no other
- command is active and allocation is guaranteed to succeed.
-
Once allocated qc's taskfile is initialized for the command to be
executed. qc currently has two mechanisms to notify completion. One
is via ``qc->complete_fn()`` callback and the other is completion
@@ -447,11 +441,6 @@ SCSI commands
translated. No qc is involved in processing a simulated scmd. The
result is computed right away and the scmd is completed.

- For a translated scmd, :c:func:`ata_qc_new_init` is invoked to allocate a
- qc and the scmd is translated into the qc. SCSI midlayer's
- completion notification function pointer is stored into
- ``qc->scsidone``.
-
``qc->complete_fn()`` callback is used for completion notification. ATA
commands use :c:func:`ata_scsi_qc_complete` while ATAPI commands use
:c:func:`atapi_qc_complete`. Both functions end up calling ``qc->scsidone``
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 0c854aebfe0bdc..811fceb4e647fa 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4563,42 +4563,6 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
#endif /* __BIG_ENDIAN */
}

-/**
- * ata_qc_new_init - Request an available ATA command, and initialize it
- * @dev: Device from whom we request an available command structure
- * @tag: tag
- *
- * LOCKING:
- * None.
- */
-
-struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag)
-{
- struct ata_port *ap = dev->link->ap;
- struct ata_queued_cmd *qc;
-
- /* no command while frozen */
- if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
- return NULL;
-
- /* libsas case */
- if (ap->flags & ATA_FLAG_SAS_HOST) {
- tag = ata_sas_allocate_tag(ap);
- if (tag < 0)
- return NULL;
- }
-
- qc = __ata_qc_from_tag(ap, tag);
- qc->tag = qc->hw_tag = tag;
- qc->scsicmd = NULL;
- qc->ap = ap;
- qc->dev = dev;
-
- ata_qc_reinit(qc);
-
- return qc;
-}
-
/**
* ata_qc_free - free unused ata_queued_cmd
* @qc: Command to complete
@@ -4611,19 +4575,9 @@ struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag)
*/
void ata_qc_free(struct ata_queued_cmd *qc)
{
- struct ata_port *ap;
- unsigned int tag;
-
- WARN_ON_ONCE(qc == NULL); /* ata_qc_from_tag _might_ return NULL */
- ap = qc->ap;
-
qc->flags = 0;
- tag = qc->tag;
- if (ata_tag_valid(tag)) {
+ if (ata_tag_valid(qc->tag))
qc->tag = ATA_TAG_POISON;
- if (ap->flags & ATA_FLAG_SAS_HOST)
- ata_sas_free_tag(tag, ap);
- }
}

void __ata_qc_complete(struct ata_queued_cmd *qc)
diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
index 071158c0c44c1d..13e2c0d28b6937 100644
--- a/drivers/ata/libata-sata.c
+++ b/drivers/ata/libata-sata.c
@@ -1268,31 +1268,6 @@ int ata_sas_queuecmd(struct scsi_cmnd *cmd, struct ata_port *ap)
}
EXPORT_SYMBOL_GPL(ata_sas_queuecmd);

-int ata_sas_allocate_tag(struct ata_port *ap)
-{
- unsigned int max_queue = ap->host->n_tags;
- unsigned int i, tag;
-
- for (i = 0, tag = ap->sas_last_tag + 1; i < max_queue; i++, tag++) {
- tag = tag < max_queue ? tag : 0;
-
- /* the last tag is reserved for internal command. */
- if (ata_tag_internal(tag))
- continue;
-
- if (!test_and_set_bit(tag, &ap->sas_tag_allocated)) {
- ap->sas_last_tag = tag;
- return tag;
- }
- }
- return -1;
-}
-
-void ata_sas_free_tag(unsigned int tag, struct ata_port *ap)
-{
- clear_bit(tag, &ap->sas_tag_allocated);
-}
-
/**
* sata_async_notification - SATA async notification handler
* @ap: ATA port where async notification is received
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index ed8be585a98f7c..5e0bc7b05a107e 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -638,24 +638,44 @@ EXPORT_SYMBOL_GPL(ata_scsi_ioctl);
static struct ata_queued_cmd *ata_scsi_qc_new(struct ata_device *dev,
struct scsi_cmnd *cmd)
{
+ struct ata_port *ap = dev->link->ap;
struct ata_queued_cmd *qc;
+ int tag;

- qc = ata_qc_new_init(dev, scsi_cmd_to_rq(cmd)->tag);
- if (qc) {
- qc->scsicmd = cmd;
- qc->scsidone = scsi_done;
-
- qc->sg = scsi_sglist(cmd);
- qc->n_elem = scsi_sg_count(cmd);
+ if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
+ goto fail;

- if (scsi_cmd_to_rq(cmd)->rq_flags & RQF_QUIET)
- qc->flags |= ATA_QCFLAG_QUIET;
+ if (ap->flags & ATA_FLAG_SAS_HOST) {
+ /* XXX: add a comment here why SAS is different */
+ if (WARN_ON_ONCE(cmd->budget_token >= ATA_MAX_QUEUE))
+ goto fail;
+ tag = cmd->budget_token;
} else {
- cmd->result = (DID_OK << 16) | SAM_STAT_TASK_SET_FULL;
- scsi_done(cmd);
+ tag = scsi_cmd_to_rq(cmd)->tag;
}

+ qc = __ata_qc_from_tag(ap, tag);
+ qc->tag = qc->hw_tag = tag;
+ qc->scsicmd = NULL;
+ qc->ap = ap;
+ qc->dev = dev;
+
+ ata_qc_reinit(qc);
+
+ qc->scsicmd = cmd;
+ qc->scsidone = scsi_done;
+
+ qc->sg = scsi_sglist(cmd);
+ qc->n_elem = scsi_sg_count(cmd);
+
+ if (scsi_cmd_to_rq(cmd)->rq_flags & RQF_QUIET)
+ qc->flags |= ATA_QCFLAG_QUIET;
return qc;
+
+fail:
+ cmd->result = (DID_OK << 16) | SAM_STAT_TASK_SET_FULL;
+ scsi_done(cmd);
+ return NULL;
}

static void ata_qc_set_pc_nbytes(struct ata_queued_cmd *qc)
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index 51e01acdd24107..191f8bfe038656 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -44,7 +44,6 @@ static inline void ata_force_cbl(struct ata_port *ap) { }
#endif
extern u64 ata_tf_to_lba(const struct ata_taskfile *tf);
extern u64 ata_tf_to_lba48(const struct ata_taskfile *tf);
-extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev, int tag);
extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
u64 block, u32 n_block, unsigned int tf_flags,
unsigned int tag, int class);
@@ -91,18 +90,6 @@ extern unsigned int ata_read_log_page(struct ata_device *dev, u8 log,

#define to_ata_port(d) container_of(d, struct ata_port, tdev)

-/* libata-sata.c */
-#ifdef CONFIG_SATA_HOST
-int ata_sas_allocate_tag(struct ata_port *ap);
-void ata_sas_free_tag(unsigned int tag, struct ata_port *ap);
-#else
-static inline int ata_sas_allocate_tag(struct ata_port *ap)
-{
- return -EOPNOTSUPP;
-}
-static inline void ata_sas_free_tag(unsigned int tag, struct ata_port *ap) { }
-#endif
-
/* libata-acpi.c */
#ifdef CONFIG_ATA_ACPI
extern unsigned int ata_acpi_gtf_filter;
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 7f99b4d788223b..3b9399f67b3902 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -814,7 +814,6 @@ struct ata_port {
unsigned int cbl; /* cable type; ATA_CBL_xxx */

struct ata_queued_cmd qcmd[ATA_MAX_QUEUE + 1];
- unsigned long sas_tag_allocated; /* for sas tag allocation only */
u64 qc_active;
int nr_active_links; /* #links with active qcs */
unsigned int sas_last_tag; /* track next tag hw expects */