Re: [PATCH 8/8] scsi: libsas: support SATA phy link rate unmatch the pathway

[Jason Yan]

On 2018/6/1 0:05, John Garry wrote:
> On 29/05/2018 03:23, Jason Yan wrote:
> > If a SATA disk attached to a expander phy and it's linkrate is greater
> > than the expander host phy's linkrate, the disk will failed to discover.
> > The topology is like below:
> >
> >    +----------+           +----------+
> >    |          |           |          |
> >    |          |-- 3.0 G --|          |-- 6.0 G -- SAS  disk
> >    |          |           |          |
> >    |          |-- 3.0 G --|          |-- 6.0 G -- SAS  disk
> >    |initiator |           |          |
> >    | device   |-- 3.0 G --| Expander |-- 6.0 G -- SAS  disk
> >    |          |           |          |
> >    |          |-- 3.0 G --|          |-- 6.0 G -- SATA disk  -->failed
> > to connect
> >    |          |           |          |
> >    |          |           |          |-- 6.0 G -- SATA disk  -->failed
> > to connect
> >    |          |           |          |
> >    +----------+           +----------+
> >
> > And when we check the sas protocal spec, this scenario is described as
> > this:
> >
> > 7.13 Rate matching
> > ......
> > If an expander phy attached to a SATA phy is using a physical link rate
> > greater than the maximum connection rate supported by the pathway from
> > an STP initiator port, a management application client should use the
> > SMP PHY CONTROL function (see 10.4.3.10) to set the PROGRAMMED MAXIMUM
> > PHYSICAL LINK RATE field of the expander phy to the maximum connection
> > rate supported by the pathway from that STP initiator port.
> >
> > In order to support this scenario, checking the SATA disk's linkrate
> > to see if it is greater than any phy's linkrate it may pass through.
> > Remember the minimum linkrate of the pathway and set the SATA phy
> > linkrate to it using the SMP PHY CONTROL function.
>
> As we (re)discover the tree, can we keep track of the min pathway to the
> root PHY dynamically (per expander), and then take action for any SATA
> devices attached which have a negotiated linkrate greater (than the
> expanders min pathway)? This would be an alternate to your approach of
> finishing discovery and then checking the min pathway as a whole new step.

Seems better, I will have a try to see if it works. Thanks.

> .