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

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

[Frank Wunderlich]

From: Frank Wunderlich <frank-w@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@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

Re: [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@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@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?

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

[Daniel Golle]

On Thu, Apr 09, 2026 at 07:49:42PM +0300, Vladimir Oltean wrote:
> 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?

Yes, vendor SDK uses DT mediatek,pnswap{,-rx,-tx} properties only for the
SoC GMACs. For MT7531 there are **no** strap pins deciding the SerDes
polarity, and also no software-way to override the defaults in the vendor
SDK.

However, the MT7531 datasheet quite clearly states:
Register 000050EC QPHY_WRAP_CTRL -- QPHY wrapper control
Reset value: 0x00000501

BIT 1 RX_BIT_POLARITY -- RX bit polarity control
 1'b0: normal
 1'b1: inverted

BIT 0 TX_BIT_POLARITY -- TX bit polarity control (TX default inversed in MT7531)
 1'b0: normal
 1'b1: inverted

Hence the best would be to just assume the documented default in the driver
as well.

A quick register dump using the BPi-R3 confirms that this applies to *both*
SerDes PCS on MT7531A (port 5 and port 6) equally, both read 0x00000501
after reset.