linux-kernel - Re: [PATCH 2/2] net: phy: dp83826: Add support for straps reading

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Message-ID: <a545c67f-de26-4224-8d20-c8abdbd6a9c7@yoseli.org>
Date: Tue, 4 Mar 2025 07:37:00 +0100
From: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Catalin Popescu <catalin.popescu@...ca-geosystems.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: phy: dp83826: Add support for straps reading

Hello Andrew,

On 03/03/2025 18:50, Andrew Lunn wrote:
> On Mon, Mar 03, 2025 at 06:37:28PM +0100, Jean-Michel Hautbois wrote:
>> Hi Andrew,
>>
>> On 03/03/2025 18:20, Andrew Lunn wrote:
>>> On Mon, Mar 03, 2025 at 06:05:52PM +0100, Jean-Michel Hautbois wrote:
>>>> When the DP83826 is probed, read the straps, and apply the default
>>>> settings expected. The MDI-X is not yet supported, but still read the
>>>> strap.
>>>
>>> What about backwards compatibility? I expect this changes the
>>> behaviour of the device, potentially introducing regressions?  Please
>>> add an explanation of why this is safe.
>>
>> I am not certain it is safe. As far as I know that if straps are used on the
>> hardware, then it should be used, and if the behavior has to be different,
>> then userspace can change it (or any other way). Am I wrong ?
> 
> First off, what does the datasheet say about these straps?
> 
> Straps generally configure the hardware, without software being
> involved. It seems odd you need software to read the straps and apply
> them.
> 
> Why do you need this? What is your use case. As you said, user space
> can configure all this, so why are you not doing that?

Thanks you for your remarks, indeed, ip link set + ethtool -s works fine 
to force the link mode wanted. Event the master/slave can be specified, 
so there is no need for this patch 2/2.

Thanks !
JM