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libata-pmp-prep: implement ops->qc_defer()

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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>
This commit is contained in:
Tejun Heo
2007-09-23 13:14:12 +09:00
committed by Jeff Garzik
parent fb7fd61454
commit 31cc23b349
6 changed files with 67 additions and 36 deletions
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31
drivers/ata/libata-core.c
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@@ -4345,6 +4345,36 @@ int ata_check_atapi_dma(struct ata_queued_cmd *qc)
return 0;
}
/**
* 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_interrupt);
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);