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

[Paolo Abeni]

On 12/23/25 11:10 AM, Stefan Eichenberger wrote:
> From: Stefan Eichenberger <stefan.eichenberger at toradex.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 at toradex.com>

## Form letter - net-next-closed

The net-next tree is closed for new drivers, features, code refactoring
and optimizations due to the merge window and the winter break. We are
currently accepting bug fixes only.

Please repost when net-next reopens after Jan 2nd.

RFC patches sent for review only are obviously welcome at any time.