• Tejun Heo's avatar
    libata: improve phantom device detection · 6a6b97d3
    Tejun Heo authored
    Currently libata uses four methods to detect device presence.
    
    1. PHY status if available.
    2. TF register R/W test (only promotes presence, never demotes)
    3. device signature after reset
    4. IDENTIFY failure detection in SFF state machine
    
    Combination of the above works well in most cases but recently there
    have been a few reports where a phantom device causes unnecessary
    delay during probe.  In both cases, PHY status wasn't available.  In
    one case, it passed #2 and #3 and failed IDENTIFY with ATA_ERR which
    didn't qualify as #4.  The other failed #2 but as it passed #3 and #4,
    it still caused failure.
    
    In both cases, phantom device reported diagnostic failure, so these
    cases can be safely worked around by considering any !ATA_DRQ IDENTIFY
    failure as NODEV_HINT if diagnostic failure is set.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarJeff Garzik <jgarzik@redhat.com>
    6a6b97d3
libata-sff.c 72.6 KB