linux-kernel - Re: [PATCH] [SCSI] LIBSAS: fix libsas link error issue

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Message-ID: <4DF831E6.3050502@interlog.com>
Date:	Wed, 15 Jun 2011 00:15:34 -0400
From:	Douglas Gilbert <dgilbert@...erlog.com>
To:	Xiangliang Yu <yuxiangl@...vell.com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	"yxlraid@...il.com" <yxlraid@...il.com>,
	"jack_wang@...sh.com" <jack_wang@...sh.com>,
	"lucas.demarchi@...fusion.mobi" <lucas.demarchi@...fusion.mobi>,
	"maciej.trela@...el.com" <maciej.trela@...el.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jacky Feng <jfeng@...vell.com>
Subject: Re: [PATCH] [SCSI] LIBSAS: fix libsas link error issue

On 11-06-14 09:44 PM, Xiangliang Yu wrote:
> Subject: Re: [PATCH] [SCSI] LIBSAS: fix libsas link error issue
>
> On Tue, 2011-06-14 at 23:17 +0800, yxlraid@...il.com wrote:
>>> From: Xiangliang Yu<yuxiangl@...vell.com>
>>>
>>> -- 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@...vell.com>
>>> ---
>>>   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.

spl2r01.pdf [Most recent SAS-3 draft for the protocol layers]

5.7.4.2.1 SAS speed negotiation sequence overview

"The SAS speed negotiation sequence establishes communications between
the two phys on a physical link at the highest possible transmission
rate."


That seems to suggest:
    min(<one_end>.max_linkrate, <other_end>.max_linkrate)

Doug Gilbert


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