On Wed, Feb 29, 2012 at 1:55 PM, James Bottomley
[off-list ref] 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.

I don't quite understand this.  Are you saying we can't (or shouldn't)
execute

/sys/class/sas_phy/<phy-X>/hard_reset

on the root device for some reason?

The case I ran into was accidentally changing the host sas address
between reboots.  If the sata device had been a root device then I
would not have been able boot the system.  But now that I think about
it, if Linux could not boot then neither could the pre-os
option-rom/efi driver.

quoted

After the system is booted this state can be cleared via
/sys/module/libsas/parameters/force_hard_reset

I really don't think a module parameter for this is such a good idea ...
it effectively promotes all soft resets to being hard ones, which can
have a lot of unintended consequences.

Yes, it was only meant as a temporary "get out of a sticky situation"
option, but given the above pre-os-driver realization it is not even
useful for that case.  So I'm fine killing this patch.

--
Dan