netdev - Re: [PATCH net 1/2] s390/qeth: update cached link

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Date:   Thu, 4 Aug 2022 15:44:42 +0200
From:   Alexandra Winter <wintera@...ux.ibm.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Thorsten Winkler <twinkler@...ux.ibm.com>
Subject: Re: [PATCH net 1/2] s390/qeth: update cached link_info for ethtool



On 04.08.22 15:08, Andrew Lunn wrote:
> On Thu, Aug 04, 2022 at 10:53:33AM +0200, Alexandra Winter wrote:
>>
>>
>> On 03.08.22 17:19, Andrew Lunn wrote:
>>> On Wed, Aug 03, 2022 at 04:40:14PM +0200, Alexandra Winter wrote:
>>>> Speed, duplex, port type and link mode can change, after the physical link
>>>> goes down (STOPLAN) or the card goes offline
>>>
>>> If the link is down, speed, and duplex are meaningless. They should be
>>> set to DUPLEX_UNKNOWN, SPEED_UNKNOWN. There is no PORT_UNKNOWN, but
>>> generally, it does not change on link up, so you could set this
>>> depending on the hardware type.
>>>
>>> 	Andrew
>>
>> Thank you Andrew for the review. I fully understand your point.
>> I would like to propose that I put that on my ToDo list and fix
>> that in a follow-on patch to net-next.
>>
>> The fields in the link_info control blocks are used today to generate
>> other values (e.g. supported speed) which will not work with *_UNKNOWN,
>> so the follow-on patch will be more than just 2 lines.
> 
> So it sounds like your code is all backwards around. If you know what
> the hardware is, you know the supported link modes are, assuming its
> not an SFP and the SFP module is not plugged in. Those link modes
> should be independent of if the link is up or not. speed/duplex is
> only valid when the link is up and negotiation has finished.
> 
> Since this is for net, than yes, maybe it would be best to go with a
> minimal patch to make your backwards around code work. But for
> net-next, you really should fix this properly. 
> 
> 	  Andrew

Thank you Andrew. I agree with your analysis.