linux-kernel - Re: [PATCH net-next 1/8] net: phy: add support for overclocked SGMII

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Date: Wed, 19 Jun 2024 22:07:21 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, Vinod Koul <vkoul@...nel.org>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH net-next 1/8] net: phy: add support for overclocked SGMII

On Wed, Jun 19, 2024 at 09:51:12PM +0200, Andrew Lunn wrote:
> phylib supports out of band signalling, which is enough to make this
> work, so long as two peers will actually establish a link because they
> are sufficiently tolerant of what the other end is doing. Sometimes
> they need a hint. Russell King has been working on this mess, and i'm
> sure he will be along soon.

... and I'm rolling my eyes, wondering whether I will get time to
finish the code that I started any time soon. I'll note that the more
hacky code we end up merging, the harder it will become to solve this
problem (and we already have several differing behaviours merged with
2500base-X already.)

> What i expect will happen is you keep calling this 2500BaseX, without
> in band signalling. You can look back in the netdev mailling list for
> more details and those that have been here before you. It is always
> good to search the history, otherwise you are just going to repeat it.

That's where things start getting sticky, because at the moment,
phylink expects 2500base-X to be like 1000base-X, and be a media
interface mode rather than a MAC-to-PHY interface mode. This is partly
what my patches will address if I can get around to finishing them -
but at this point I really do not know when that will be.

I still have the high priority work problem that I'm actively involved
with. I may have three weeks holiday at the start of July (and I really
need it right now!) Then, there's possibly quite a lot of down time in
August because I'm having early cataract ops which will substantially
change my eye sight. There's two possible outcomes from that. The best
case is that in just over two weeks after the first op, I'll be able to
read the screen without glasses. The worst case is that I have to wait
a further two to three weeks to see my optometrist (assuming he has
availability), and then wait for replacement lenses to be made up,
fitted and the new glasses sent.

So, I'm only finding the occasional time to be able to look at
mainline stuff, and I don't see that changing very much until maybe
September.

At this point, I think we may as well give up and let people do
whatever they want to do with 2500base-X (which is basically what we're
already doing), and when they have compatibility problems... well...
really not much we can do about that, and it will be way too late to
try and sort the mess out.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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