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

[John Garry]

On 01/06/2018 02:21, Jason Yan wrote:
> 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.

Fine, it seems the tricky part here is to figure out when to issue the 
linkrate change request.