[RFC net PATCH v1] net: pcs: pcs-mtk-lynxi: fix bpi-r3 serdes configuration

[Vladimir Oltean]

On Thu, Apr 09, 2026 at 03:33:42PM +0200, Frank Wunderlich wrote:
> From: Frank Wunderlich <frank-w at public-files.de>
> 
> Commit 8871389da151 introduces common pcs dts properties which writes
> rx=normal,tx=normal polarity to register SGMSYS_QPHY_WRAP_CTRL of switch.
> This is initialized with tx-bit set and so change inverts polarity
> compared to before.
> 
> It looks like mt7531 has tx polarity inverted in hardware and set tx-bit
> by default to restore the normal polarity.
> 
> Till this patch the register write was only called when mediatek,pnswap
> property was set which cannot be done for switch because the fw-node param
> was always NULL from switch driver in the mtk_pcs_lynxi_create call.
> 
> Do not configure switch side like it's done before.
> 
> Fixes: 8871389da151 ("net: pcs: pcs-mtk-lynxi: deprecate "mediatek,pnswap"")
> Signed-off-by: Frank Wunderlich <frank-w at public-files.de>
> ---
>  drivers/net/pcs/pcs-mtk-lynxi.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/pcs/pcs-mtk-lynxi.c b/drivers/net/pcs/pcs-mtk-lynxi.c
> index c12f8087af9b..a753bd88cbc2 100644
> --- a/drivers/net/pcs/pcs-mtk-lynxi.c
> +++ b/drivers/net/pcs/pcs-mtk-lynxi.c
> @@ -129,6 +129,9 @@ static int mtk_pcs_config_polarity(struct mtk_pcs_lynxi *mpcs,
>         unsigned int val = 0;
>         int ret;
> 
> +       if (!fwnode)
> +               return 0;
> +
>         if (fwnode_property_read_bool(fwnode, "mediatek,pnswap"))
>                 default_pol = PHY_POL_INVERT;
> 
> --
> 2.43.0
>

I notice Arınc, listed by ./scripts/get_maintainer.pl drivers/net/dsa/mt7530.c,
and Felix, listed by ./scripts/get_maintainer.pl drivers/net/ethernet/mediatek/mtk_eth_soc.c,
are not on CC. Maybe they have more info.

Only the switch port has a chance of having a non-zero default polarity
setting? (coming from the efuse, if I understood this discussion properly)
https://lore.kernel.org/netdev/C59EED96-3973-4074-A4D8-C264949D447E@linux.dev/
The GMAC doesn't?