RE: [PATCH] [SCSI] LIBSAS: fix libsas link error issue

[Xiangliang Yu]

On Tue, 2011-06-14 at 18:44 -0700, Xiangliang Yu wrote:
>> Subject: Re: [PATCH] [SCSI] LIBSAS: fix libsas link error issue
>> 
>> On Tue, 2011-06-14 at 23:17 +0800, yxlraid@xxxxxxxxx wrote:
>> >> From: Xiangliang Yu <yuxiangl@xxxxxxxxxxx>
>> >> 
>> >> -- The value of child link rate should is minimum of link rate, or
>> >>    command will fail if child link rate is bigger than parent link rate.
>> >> 
>> >> Signed-off-by: Xiangliang Yu <yuxiangl@xxxxxxxxxxx>
>> >> ---
>> >>  drivers/scsi/libsas/sas_expander.c |    2 +-
>> >>  1 files changed, 1 insertions(+), 1 deletions(-)
>> >> 
>> >> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
>> >> index 874e29d..6ccca09 100644
>> >> --- a/drivers/scsi/libsas/sas_expander.c
>> >> +++ b/drivers/scsi/libsas/sas_expander.c
>> >> @@ -638,7 +638,7 @@ static void sas_ex_get_linkrate(struct domain_device *parent,
>> >>  			sas_port_add_phy(port, phy->phy);
>> >>  		}
>> >>  	}
>> >> -	child->linkrate = min(parent_phy->linkrate, child->max_linkrate);
>> >> +	child->linkrate = min(parent_phy->linkrate, child->min_linkrate);
>> 
>> >This patch doesn't look right.  It will clamp the phy to the minim
>> >possible link rate.  
>> Link negotiation should get the minimum.

>it's probably a negotiation problem.  If the
>child can't support the highest possible link rate because of problems
>like transmission errors, it should fall back.

I get the issue like this: 
1. HBA support 3Gbps, level 1 expander support 6Gbps, and level 2 expander support 6Gbps; 
2. level 1 is fine, and find that level 2 link rate is 6Gbps in DISCOVER command response.
3. LIBSAS think level 2 is 6Gbps by sas_ex_get_linkrate function, and send command to level 2 expander
4. LIBSAS link error.

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