linux-kernel - [PATCH net 1/2] net: pcs: xpcs: fix DW_VR_MII_DIG_CTRL1_2G5

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Message-Id: <20250114164721.2879380-1-vladimir.oltean@nxp.com>
Date: Tue, 14 Jan 2025 18:47:20 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: Jose Abreu <Jose.Abreu@...opsys.com>,
	Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
	Voon Weifeng <weifeng.voon@...el.com>,
	Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH net 1/2] net: pcs: xpcs: fix DW_VR_MII_DIG_CTRL1_2G5_EN bit being set for 1G SGMII w/o inband

On a port with SGMII fixed-link at SPEED_1000, DW_VR_MII_DIG_CTRL1 gets
set to 0x2404. This is incorrect, because bit 2 (DW_VR_MII_DIG_CTRL1_2G5_EN)
is set.

It comes from the previous write to DW_VR_MII_AN_CTRL, because the "val"
variable is reused and is dirty. Actually, its value is 0x4, aka
FIELD_PREP(DW_VR_MII_PCS_MODE_MASK, DW_VR_MII_PCS_MODE_C37_SGMII).

Resolve the issue by clearing "val" to 0 when writing to a new register.
After the fix, the register value is 0x2400.

Prior to the blamed commit, when the read-modify-write was open-coded,
the code saved the content of the DW_VR_MII_DIG_CTRL1 register in the
"ret" variable.

Fixes: ce8d6081fcf4 ("net: pcs: xpcs: add _modify() accessors")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/pcs/pcs-xpcs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index e270a75a988c..3de0a25a1eca 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -728,6 +728,7 @@ static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs,
 	if (ret < 0)
 		return ret;

+	val = 0;
 	mask = DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW;
 	if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED)
 		val = DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW;
-- 
2.34.1