linux-kernel - Re: [PATCH] phy: aquantia: Configure SERDES mode by default

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Date:   Tue, 15 Nov 2022 17:46:54 -0500
From:   Sean Anderson <sean.anderson@...o.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        Tim Harvey <tharvey@...eworks.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH] phy: aquantia: Configure SERDES mode by default

On 11/15/22 17:37, Vladimir Oltean wrote:
> On Mon, Nov 14, 2022 at 04:07:39PM -0500, Sean Anderson wrote:
>> When autonegotiation completes, the phy interface will be set based on
>> the global config register for that speed. If the SERDES mode is set to
>> something which the MAC does not support, then the link will not come
>> up. The register reference says that the SERDES mode should default to
>> XFI, but for some phys lower speeds default to XFI/2 (5G XFI). To ensure
>> the link comes up correctly, configure the SERDES mode.
>> 
>> We use the same configuration for all interfaces. We don't advertise
>> any speeds faster than the interface mode, so they won't be selected.
>> We default to pause-based rate adaptation, but enable USXGMII rate
>> adaptation for USXGMII. I'm not sure if this is correct for
>> SGMII; it might need USXGMII adaptation instead.
>> 
>> This effectively disables switching interface mode depending on the
>> speed, in favor of using rate adaptation. If this is not desired, we
>> would need some kind of API to configure things.
>> 
>> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
>> ---
> 
> Was this patch tested and confirmed to do something sane on any platform
> at all?

This was mainly intended for Tim to test and see if it fixed his problem.

--Sean