[PATCHSET] prep for PMP support, take 3

[Tejun Heo <htejun@gmail.com>]

Hello, all.

This is the third take of libata-pmp-prep patchset.  This patchset
contains 5 patches and implements various stuff needed for PMP.

Changes from the last take[L] are.

* rebased
* sata_link_hardreset() separation is done earlier by vt8251-ahci
  patchset and thus dropped from this patchset.

This patchset is against

  upstream (da54f5fe54c7d75e2db7d17961fb36a8c28a8501)
  + [1] hp-poll patchset, take #5
  + [2] vt8251-ahci patchset, take #2
  + [3] libata-link patchset, take #3

Git tree can be accessed at

  http://htj.dyndns.org/git/?p=libata-tj.git;a=shortlog;h=pmp-prep
  git://htj.dyndns.org/libata-tj pmp-prep

Jeff, I couldn't merge ->qc_defer() into ->qc_prep() or ->qc_issue().
The problem is that ->qc_prep() is done after sg mapping is done which
is a bit costly to throw away if the qc has to be deferred.
->qc_defer() is called right after qc is allocated and translated but
before any resource for qc execution is acuquired.

Another way would be to let ->qc_issue() determine whether deferring
is needed and cache prepared qc while deferred.  This has the
following problems.

* qc and related resources are held by deferred command.  Currently,
  qc directly maps to hardware command slots and w/ PMP this can get
  messy.

* Separate requeueing/restarting mechanism must be implemented.  ATM,
  libata depends on SCSI for retrying deferred commands with
  reasonable fairness.  To hold prepared qc, libata needs to implement
  its own mechanism and I don't think the added benefits justify the
  complexity.

So, I think it's better to keep ->qc_defer().

Thanks.

--
tejun

[L] http://article.gmane.org/gmane.linux.ide/11928
[1] http://article.gmane.org/gmane.linux.ide/13467
[2] http://article.gmane.org/gmane.linux.ide/13471
[3] http://article.gmane.org/gmane.linux.ide/13478