Re: [PATCH 3.12 81/94] libata: support the ata host which implements a queue depth less than 32

[Thomas Backlund <tmb@mageia.org>]

Jiri Slaby skrev den 30.7.2014 15:15:
> From: Kevin Hao <haokexin@gmail.com>
>
> 3.12-stable review patch.  If anyone has any objections, please let me know.
>
> ===============
>
> commit 1871ee134b73fb4cadab75752a7152ed2813c751 upstream.
>
> The sata on fsl mpc8315e is broken after the commit 8a4aeec8d2d6
> ("libata/ahci: accommodate tag ordered controllers"). The reason is
> that the ata controller on this SoC only implement a queue depth of
> 16. When issuing the commands in tag order, all the commands in tag
> 16 ~ 31 are mapped to tag 0 unconditionally and then causes the sata
> malfunction. It makes no senses to use a 32 queue in software while
> the hardware has less queue depth. So consider the queue depth
> implemented by the hardware when requesting a command tag.
>
> Fixes: 8a4aeec8d2d6 ("libata/ahci: accommodate tag ordered controllers")
> Signed-off-by: Kevin Hao <haokexin@gmail.com>
> Acked-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>

As you have added this to 3.12 branch, you also need to add this to 
avoid SAS breakage:

commit 1a112d10f03e83fb3a2fdc4c9165865dec8a3ca6
Author: Tejun Heo <tj@kernel.org>
Date:   Wed Jul 23 09:05:27 2014 -0400

     libata: introduce ata_host->n_tags to avoid oops on SAS controllers

     1871ee134b73 ("libata: support the ata host which implements a queue
     depth less than 32") directly used ata_port->scsi_host->can_queue from
     ata_qc_new() to determine the number of tags supported by the host;
     unfortunately, SAS controllers doing SATA don't initialize ->scsi_host
     leading to the following oops.

--

Thomas