On 12-02-29 04:55 PM, James Bottomley wrote:

On Fri, 2012-02-10 at 00:45 -0800, Dan Williams wrote:

quoted

It is possible for a host to get "locked out" from talking to sata
devices in the domain if, for example, its sas address changes but the
expander topology has existing affiliations with the old address.  If
the system is booted userspace can write to
/sys/class/sas_phy/<phy-X>/hard_reset to clear the affiliation, however
if this condition exists for the root device the module parameter can be
used to promote all ata resets to hard resets.

A point of order: SAS has link resets and hard resets. The
hard reset is a superset of link reset. A "link reset sequence
serves as a hard reset for SATA devices" and hence is
sufficient to reset a SATA device. To reset a SAS device
(e.g. a SAS disk) you need a SAS hard reset. Therefore a link
reset is the appropriately sized "gun" to reset a SATA device.

I have a SAS-2 expander that annoyingly powers up with the
programmed maximum physical link rate of its phys at 3 Gbps
even though its hardware maximum rate is 6 Gbps. For expander
phys connected to SAS-2 disks I can up the programmed maximum
value to 6 Gbps on the expander phy then do a link reset on
that phy. So without upsetting Linux (or any other OS) I can
switch that path from 3 Gbps to 6 Gbps. Can't do that with a
SATA disk without the OS finding out.

Also to clear a SATA affiliation you should be using a SMP
PHY CONTROL (phy_op=6) function.

Doug Gilbert