linux-kernel - Re: [PATCH net] net: phy: Don't assume loopback is supported

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Message-ID: <07dd8427-4779-1706-3c0a-17ae58939c41@synopsys.com>
Date:   Mon, 18 Mar 2019 12:46:09 +0000
From:   Jose Abreu <jose.abreu@...opsys.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>
CC:     Florian Fainelli <f.fainelli@...il.com>,
        Jose Abreu <jose.abreu@...opsys.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Joao Pinto <joao.pinto@...opsys.com>
Subject: Re: [PATCH net] net: phy: Don't assume loopback is supported

Hi Andrew and Heiner,

On 3/17/2019 6:38 PM, Andrew Lunn wrote:
> On Fri, Mar 15, 2019 at 03:48:41PM -0700, Florian Fainelli wrote:
>> On 3/14/19 3:37 AM, Jose Abreu wrote:
>>> Some PHYs may not support loopback mode so we need to check if register
>>> is read-only.
>>>
>>
>> In that case it may be appropriate to have a specific PHY driver that
>> implements a set_loopback() method returning -EOPNOTSUPP instead of
>> changing the generic PHY implementation.
> 
> Hi Jose
> 
> Since Heiner says this is a mandatory feature, we should not really
> penalise conformant PHYs just because there is one broken PHY.

We provide PHYs to our customers and in the documentation I have
this can be an optional feature that HW team can choose to have
or not, making the bit read-only or r/w.

Heiner, can you please confirm there is no Clause 22 "pitfalls" /
"hidden comments" that allow this bitfield to be read-only ?

Thanks,
Jose Miguel Abreu