netdev - Re: [PATCH net-next v5 0/4] phy: aquantia: Determine rate adaptation support from registers

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Date:   Thu, 5 Jan 2023 11:25:31 -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>, netdev@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Tim Harvey <tharvey@...eworks.com>
Subject: Re: [PATCH net-next v5 0/4] phy: aquantia: Determine rate adaptation
 support from registers

On 1/5/23 08:39, Vladimir Oltean wrote:
> Hi Sean,
> 
> On Tue, Jan 03, 2023 at 05:05:07PM -0500, Sean Anderson wrote:
>> This attempts to address the problems first reported in [1]. Tim has an
>> Aquantia phy where the firmware is set up to use "5G XFI" (underclocked
>> 10GBASE-R) when rate adapting lower speeds. This results in us
>> advertising that we support lower speeds and then failing to bring the
>> link up. To avoid this, determine whether to enable rate adaptation
>> based on what's programmed by the firmware. This is "the worst choice"
>> [2], but we can't really do better until we have more insight into
>> what the firmware is doing. At the very least, we can prevent bad
>> firmware from causing us to advertise the wrong modes.
> 
> After this patch set, is there any reason why phydev->rate_matching
> still exists and must be populated by the PHY driver?

It's necessary for phylink_link_up to know what speed to use for the MAC.

--Sean