linux-kernel - Re: [PATCH net-next v1 2/3] dt-bindings: net: micrel: Add keep-preamble-before-sfd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aUK-h6jDsng0Awjm@eichest-laptop>
Date: Wed, 17 Dec 2025 15:30:31 +0100
From: Stefan Eichenberger <eichest@...il.com>
To: Rob Herring <robh@...nel.org>
Cc: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, krzk+dt@...nel.org,
	conor+dt@...nel.org, hkallweit1@...il.com, linux@...linux.org.uk,
	geert+renesas@...der.be, ben.dooks@...ethink.co.uk,
	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, francesco.dolcini@...adex.com,
	rafael.beims@...adex.com,
	Stefan Eichenberger <stefan.eichenberger@...adex.com>
Subject: Re: [PATCH net-next v1 2/3] dt-bindings: net: micrel: Add
 keep-preamble-before-sfd

On Wed, Dec 17, 2025 at 07:55:19AM -0600, Rob Herring wrote:
> On Wed, Dec 17, 2025 at 01:21:19PM +0100, Stefan Eichenberger wrote:
> > On Wed, Dec 17, 2025 at 10:58:54AM +0100, Stefan Eichenberger wrote:
> > > On Mon, Dec 15, 2025 at 08:03:30AM -0600, Rob Herring wrote:
> > > > On Fri, Dec 12, 2025 at 09:46:17AM +0100, Stefan Eichenberger wrote:
> > > > > From: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > > > > 
> > > > > Add a property to activate a Micrel PHY feature that keeps the preamble
> > > > > enabled before the SFD (Start Frame Delimiter) is transmitted.
> > > > > 
> > > > > This allows to workaround broken Ethernet controllers as found on the
> > > > > NXP i.MX8MP. Specifically, errata ERR050694 that states:
> > > > > ENET_QOS: MAC incorrectly discards the received packets when Preamble
> > > > > Byte does not precede SFD or SMD.
> > > > 
> > > > It doesn't really work right if you have to change the DT to work-around 
> > > > a quirk in the kernel. You should have all the information needed 
> > > > already in the DT. The compatible string for the i.MX8MP ethernet 
> > > > controller is not sufficient? 
> > > 
> > > Is doing something like this acceptable in a phy driver?
> > > if (of_machine_is_compatible("fsl,imx8mp")) {
> > > ...
> > > }
> > > 
> > > That would be a different option, rather than having to add a new DT
> > > property. Unfortunately, the workaround affects the PHY rather than the
> > > MAC driver. This is why we considered adding a DT property.
> > 
> > Francesco made a good point about this. The i.MX8MP has two MACs, but
> > only one of them is affected. Therefore, checking the machine's
> > compatible string would not be correct. As far as I know, checking the
> > MAC's compatible string from within the PHY driver is also not good
> > practice, is it?
> 
> It's not great, but probably what you need to do. The 2 MACs are the 
> same (compatible) or different? As that only works if they are 
> different. I suppose you need to only check the MAC the PHY is connected 
> to.
> 
> I think the ideal implementation would be the MAC driver calling some 
> phy API to apply the quirk, and then that gets passed on to the phy 
> driver. Surely this isn't the first case of a MAC-PHY combination 
> needing to go fiddle with some special setting.

I was also hoping to find something like that, but I couldn't really
find it. However, I will try looking in that direction. At least we can
identify the broken MAC via the compatible string of the MAC driver, as
they use two different compatibles: 'fsl,imx8mp-fec' (fine) and
'nxp,imx8mp-dwmac-eqos' (affected by the errata).

Regards,
Stefan