linux-kernel - Re: [PATCH net-next v3 0/3] net: stmmac: dwmac: enforce preamble before SFD for i.MX8MP

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Message-ID: <af8c2609-59ca-4573-af4b-b08563a5a0bb@bootlin.com>
Date: Wed, 21 Jan 2026 11:07:25 +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, mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
 shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
 festevam@...il.com, hkallweit1@...il.com, linux@...linux.org.uk,
 linux-stm32@...md-mailman.stormreply.com, francesco.dolcini@...adex.com
Cc: netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 0/3] net: stmmac: dwmac: enforce preamble
 before SFD for i.MX8MP

Hi Stefan,

On 20/01/2026 21:30, Stefan Eichenberger wrote:
> This series adds a new phy_device flag PHY_F_KEEP_PREAMBLE_BEFORE_SFD
> that allows a MAC driver to request to keep the preamble bytes before
> the start frame delimiter (SFD) when receiving frames from the PHY.
> 
> This flag is set in the stmmac driver for the i.MX8MP SoC due to errata
> (ERR050694), which causes it to drop frames without a preamble.
> 
> The Micrel KSZ9131 PHY supports keeping the preamble before SFD by
> setting an undocumented flag, that was confirmed by NXP and Micrel. This
> new feature has been added to the Micrel PHY driver for the KSZ9131 PHY.
> 
> Changes since v2:
> - Instead of using phy_register_fixup add a new phy_device::dev_flags
>   flag PHY_F_KEEP_PREAMBLE_BEFORE_SFD so that a MAC can request to keep
>   the preamble before SFD if needed (Russell)
> - Link to v2: https://lore.kernel.org/all/20260105100245.19317-1-eichest@gmail.com/
> 
> Changes since v1:
> - Use phy_register_fixup_for_uid() instead of adding a new device tree
>   property
> - I will send the conversion of the micrel.txt binding as a separate
>   patch series
> - Link to v1: https://lore.kernel.org/all/20251212084657.29239-1-eichest@gmail.com/
> 
> Stefan Eichenberger (3):
>   net: phy: add a new phy_device flag to keep preamble before sfd
>   net: phy: micrel: add option to keep the preamble before sfd for
>     KSZ9131
>   net: stmmac: dwmac-imx: keep preamble before sfd on i.MX8MP
> 
>  drivers/net/ethernet/stmicro/stmmac/dwmac-imx.c   |  6 +++++-
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |  8 +++++++-
>  drivers/net/phy/micrel.c                          | 14 +++++++++++++-
>  include/linux/phy.h                               |  5 +++--
>  include/linux/stmmac.h                            |  1 +
>  5 files changed, 29 insertions(+), 5 deletions(-)
> 

Thank you for that. The code looks fine to me. I've tested in on a custom baord
I have that happens to have an iMX8MP and a KSZ9131, it fixes the issue for
10M links ! Thank you :)

For the series,

Tested-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@...tlin.com>

Maxime