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

[Douglas Gilbert <dgilbert@interlog.com>]

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@gmail.com wrote:
>>> From: Xiangliang Yu<yuxiangl@marvell.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@marvell.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