• Tejun Heo's avatar
    libata-pmp-prep: implement ops->qc_defer() · 31cc23b3
    Tejun Heo authored
    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
    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: default avatarTejun Heo <htejun@gmail.com>
    Signed-off-by: default avatarJeff Garzik <jeff@garzik.org>
ahci.c 50.8 KB