netdev - Re: mvneta: SGMII fixed-link not so fixed

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Date:	Fri, 18 Sep 2015 10:30:42 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Stas Sergeev <stsp@...t.ru>
CC:	andrew@...n.ch, David Miller <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: mvneta: SGMII fixed-link not so fixed

On 18/09/15 10:22, Russell King - ARM Linux wrote:
> On Fri, Sep 18, 2015 at 07:04:09PM +0300, Stas Sergeev wrote:
>> 18.09.2015 18:43, Russell King - ARM Linux пишет:
>>> On Fri, Sep 18, 2015 at 05:45:27PM +0300, Stas Sergeev wrote:
>>>> AFAICS if it has use_inband_status==true,
>>>> then it went through of_phy_register_fixed_link(dn),
>>>
>>> That's totally incorrect.  The test for setting use_inband_status in
>>> mvneta is:
>>>
>>>         err = of_property_read_string(dn, "managed", &managed);
>>>         pp->use_inband_status = (err == 0 &&
>>>                                  strcmp(managed, "in-band-status") == 0);
>>
>> Arrrr! I was looking at the branch without the last
>> patch applied, so it occurred to me as
>>
>> 	pp->use_inband_status = (phy_mode == PHY_INTERFACE_MODE_SGMII) &&
>> 		fixed_phy;
>>
>> Sorry for that.
> 
> Yay :)
> 
>> So we seem to indeed have a nasty regression with the patch
>> that just went to stable. :( Great news.
> 
> Yes.
> 
>> Thanks for you time.
>>
>> I still have problems with this part though:
>>> If there's neither a MDIO PHY nor a fixed-link, then the network driver
>>> fails to initialise the device.
>>
>> I think I am looking into the right source this time, seems like
>> if we don't have both but still have managed="in-band-status", that
>> should go the fixed-link path and still work... no?
> 
> If we have no fixed-link and no phy, then you're correct.
> 
> However, I really don't like the idea of abusing "fixed-link" as a
> method to generate an ethtool/miitool/miidiag compatible output for
> this, but I'm willing to let that pass for the moment. :)

It is not just for that, you get all the goodies from the PHY library
without modifying your Ethernet MAC driver specifically for it:
phy_connect, adjust_link and phy_ethtool_{set,get}.

The solution that was judged being the less intrusive back then was to
provide MII-like registers, getting you all user-land to work
transparently for free, but now that I think about it, having this "MII"
translation seems a bit unnecessary, if not confusing. It may be better
to remove some of register update logic and just assign phydev members
directly...
-- 
Florian
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