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

    >
    > .
    >

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