netdev - Re: [PATCH net-next 1/2] net: phy: aquantia: validate PHY mode on AQR107

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Date: Fri, 17 Nov 2023 12:46:18 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Robert Marko <robimarko@...il.com>
Cc: andrew@...n.ch, hkallweit1@...il.com, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	ansuelsmth@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] net: phy: aquantia: validate PHY mode on
 AQR107

On Fri, Nov 17, 2023 at 11:09:48AM +0100, Robert Marko wrote:
> The Aquantia driver is not setting the PHY mode itself, but it does however
> still check if the PHY mode set in DTS is one of the supported modes.
> 
> However, the set PHY mode does not have to match the actual one, so lets
> add update the PHY mode during .config_init and warn if they differ.

This looks completely wrong to me. These PHYs can be configured to
change their MAC-facing interface mode according to the media negotiated
speed, but you are only checking that _if_ the media is up, then the
interface that has resulted from that negotiation matches what is in
DTS. That could be dependent on the link partner, so what works for a
platform when connected to one link partner may issue your "info"-level
warning when connected to a different link partner.

So no, this to me looks completely wrong.

You need to check the VEND1_GLOBAL_CFG_* registers, and determine from
those what interface mode(s) will be used, and then use that to validate
the mode.

It just so happens that...

http://git.armlinux.org.uk/cgit/linux-arm.git/commit/?h=net-queue&id=f7b531ee8855f81d267a8a42c44da51576f48daf
http://git.armlinux.org.uk/cgit/linux-arm.git/commit/?h=net-queue&id=f55389aa5d11da8a32dfd65a1b98049878ce09f0

builds a bitmap that can then be tested to check this. Whether the
above is entirely correct or not, I can't really say, I don't have
enough information on this PHY.

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