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

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Date:   Fri, 1 Jun 2018 09:21:44 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     John Garry <john.garry@...wei.com>, <martin.petersen@...cle.com>,
        <jejb@...ux.vnet.ibm.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <zhaohongjiang@...wei.com>, <hare@...e.com>,
        <dan.j.williams@...el.com>, <jthumshirn@...e.de>, <hch@....de>,
        <huangdaode@...ilicon.com>, <chenxiang66@...ilicon.com>,
        <xiexiuqi@...wei.com>, <tj@...nel.org>, <miaoxie@...wei.com>,
        chenqilin <chenqilin2@...wei.com>,
        Ewan Milne <emilne@...hat.com>, Tomas Henzl <thenzl@...hat.com>
Subject: Re: [PATCH 8/8] scsi: libsas: support SATA phy link rate unmatch the
 pathway



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.

>
> .
>