libata-pmp-prep: implement ops->qc_defer()
Controllers which support PMP have various restrictions on which
combinations of commands are allowed to what number of devices
concurrently. This patch implements ops->qc_defer() which determines
whether a qc can be issued at the moment or should be deferred.
If the function returns ATA_DEFER_LINK, the qc will be deferred until
a qc completes on the link. If ATA_DEFER_PORT, until a qc completes
on any link. The defer conditions are advisory and in general
ATA_DEFER_LINK can be considered as lower priority deferring than
ATA_DEFER_PORT.
ops->qc_defer() replaces fixed ata_scmd_need_defer(). For standard
NCQ/non-NCQ exclusion, ata_std_qc_defer() is implemented. ahci and
sata_sil24 are converted to use ata_std_qc_defer().
ops->qc_defer() is heavier than the original mechanism because full qc
is prepped before determining to defer it, but various information is
needed to determine defer conditinos and fully translating a qc is the
only way to supply such information in generic manner.
IMHO, this shouldn't cause any noticeable performance issues as
* for most cases deferring occurs rarely (except for NCQ-aware
cmd-switching PMP)
* translation itself isn't that expensive
* once deferred the command won't be repeated until another command
completes which usually is a very long time cpu-wise.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 9467c2f..b666f51 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4346,6 +4346,36 @@
}
/**
+ * ata_std_qc_defer - Check whether a qc needs to be deferred
+ * @qc: ATA command in question
+ *
+ * Non-NCQ commands cannot run with any other command, NCQ or
+ * not. As upper layer only knows the queue depth, we are
+ * responsible for maintaining exclusion. This function checks
+ * whether a new command @qc can be issued.
+ *
+ * LOCKING:
+ * spin_lock_irqsave(host lock)
+ *
+ * RETURNS:
+ * ATA_DEFER_* if deferring is needed, 0 otherwise.
+ */
+int ata_std_qc_defer(struct ata_queued_cmd *qc)
+{
+ struct ata_link *link = qc->dev->link;
+
+ if (qc->tf.protocol == ATA_PROT_NCQ) {
+ if (!ata_tag_valid(link->active_tag))
+ return 0;
+ } else {
+ if (!ata_tag_valid(link->active_tag) && !link->sactive)
+ return 0;
+ }
+
+ return ATA_DEFER_LINK;
+}
+
+/**
* ata_qc_prep - Prepare taskfile for submission
* @qc: Metadata associated with taskfile to be prepared
*
@@ -7111,6 +7141,7 @@
EXPORT_SYMBOL_GPL(ata_do_set_mode);
EXPORT_SYMBOL_GPL(ata_data_xfer);
EXPORT_SYMBOL_GPL(ata_data_xfer_noirq);
+EXPORT_SYMBOL_GPL(ata_std_qc_defer);
EXPORT_SYMBOL_GPL(ata_qc_prep);
EXPORT_SYMBOL_GPL(ata_dumb_qc_prep);
EXPORT_SYMBOL_GPL(ata_noop_qc_prep);