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

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Message-ID: <bdd84dcd-3f3c-4ed6-2694-bb8252a9a266@seco.com>
Date:   Thu, 5 Jan 2023 14:10:02 -0500
From:   Sean Anderson <sean.anderson@...o.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
        "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 4/4] phy: aquantia: Determine rate adaptation
 support from registers

On 1/5/23 14:06, Russell King (Oracle) wrote:
> On Thu, Jan 05, 2023 at 01:59:27PM -0500, Sean Anderson wrote:
>> On 1/5/23 13:55, Russell King (Oracle) wrote:
>> > On Thu, Jan 05, 2023 at 07:52:06PM +0200, Vladimir Oltean wrote:
>> >> On Thu, Jan 05, 2023 at 12:43:47PM -0500, Sean Anderson wrote:
>> >> > Again, this is to comply with the existing API assumptions. The current
>> >> > code is buggy. Of course, another way around this is to modify the API.
>> >> > I have chosen this route because I don't have a situation like you
>> >> > described. But if support for that is important to you, I encourage you
>> >> > to refactor things.
>> >> 
>> >> I don't think I'm aware of a practical situation like that either.
>> >> I remember seeing some S32G boards with Aquantia PHYs which use 2500BASE-X
>> >> for 2.5G and SGMII for <=1G, but that's about it in terms of protocol switching.
>> > 
>> > 88x3310 can dynamically switch between 10GBASE-R, 5GBASE-R, 2500BASE-X
>> > and SGMII if rate adaption is not being used (and the rate adaption
>> > method it supports in non-MACSEC PHYs is only via increasing the IPG on
>> > the MAC... which currently no MAC driver supports.)
>> > 
>> 
>> As an aside, do you know of any MACs which support open-loop rate
>> matching to below ~95% of the line rate (the amount necessary for
>> 10GBASE-W)?
> 
> I'm afraid I haven't paid too much attention to BASE-W, and I'm not
> aware of anything within the realms of phylink/phylib supporting MAC
> drivers having anything for it. I don't even remember mention of it
> in any SoC datasheets.

The mEMAC supports "WAN mode" which does open-loop rate matching, but
it can really only adapt down to 9.5 GBit/s or so.

> Are you aware of a 10GBASE-W setup?

No.

--Sean