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

[Frank Wunderlich <linux@fw-web.de>]

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