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

From: Thomas Backlund
Date: Wed Jul 30 2014 - 10:56:09 EST

Jiri Slaby skrev den 30.7.2014 15:15:
From: Kevin Hao <haokexin@xxxxxxxxx>

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@xxxxxxxxx>
Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>

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@xxxxxxxxxx>
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.



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