linux-kernel - Re: [PATCH RESEND net-next v2] net: stmmac: dwmac: Add a fixup for the Micrel KSZ9131 PHY

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: <6ee0d55a-69de-4c28-8d9d-d7755d5c0808@bootlin.com>
Date: Mon, 5 Jan 2026 13:23:46 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Stefan Eichenberger <eichest@...il.com>, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, shawnguo@...nel.org, s.hauer@...gutronix.de,
 kernel@...gutronix.de, festevam@...il.com, mcoquelin.stm32@...il.com,
 alexandre.torgue@...s.st.com, linux-stm32@...md-mailman.stormreply.com
Cc: netdev@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 francesco.dolcini@...adex.com, robh@...nel.org,
 Stefan Eichenberger <stefan.eichenberger@...adex.com>
Subject: Re: [PATCH RESEND net-next v2] net: stmmac: dwmac: Add a fixup for
 the Micrel KSZ9131 PHY

Hi Stefan,

On 05/01/2026 11:02, Stefan Eichenberger wrote:
> From: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> 
> Add a fixup to the stmmac driver to keep the preamble before the SFD
> (Start Frame Delimiter) on the Micrel KSZ9131 PHY when the driver is
> used on an NXP i.MX8MP SoC.
> 
> This allows to workaround errata ERR050694 of the NXP i.MX8MP that
> states:
> ENET_QOS: MAC incorrectly discards the received packets when Preamble
> Byte does not precede SFD or SMD.
> 
> The bit which disables this feature is not documented in the datasheet
> from Micrel, but has been found by NXP and Micrel following this
> discussion:
> https://community.nxp.com/t5/i-MX-Processors/iMX8MP-eqos-not-working-for-10base-t/m-p/2151032
> 
> It has been tested on Verdin iMX8MP from Toradex by forcing the PHY to
> 10MBit. Without bit 2 being set in the remote loopback register, no
> packets are received. With the bit set, reception works fine.
> 
> Signed-off-by: Stefan Eichenberger <stefan.eichenberger@...adex.com>

I've also faced this issue, however I'm wondering wether this is the
correct approach to fix this. It seems that all Micrel / Microchip PHYs
have this behaviour of discaring the preamble at 10Mbps.

Some of these phys have accessible control registers to re-enable it,
however this register/bit changes depending on the PHY model. For
example, on KSZ8041, this is register 0x14 bit 6.

We may end-up with many many more fixups for this, basically for every
micrel/microchip PHY.

Wouldn't it be safer to just always enable preamble at 10M for these
PHYs, regardless of the MAC that's connected to it ? Is there any risk
always having the preamble there ?

Maxime