From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Nava kishore Manne <nava.kishore.manne@amd.com>,
	Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>,
	Michal Simek <michal.simek@amd.com>,
	Vinod Koul <vkoul@kernel.org>
Subject: [PATCH 5.15 341/456] phy: zynqmp: keep SERDES scrambler and 8b/10b enabled for USB
Date: Mon, 17 Aug 2026 15:32:11 +0200
Message-ID: <20260817132552.930023313@linuxfoundation.org>
In-Reply-To: <20260817132539.792407575@linuxfoundation.org>
References: <20260817132539.792407575@linuxfoundation.org>
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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nava kishore Manne <nava.kishore.manne@amd.com>

commit 7eb61caf45607e1e1270f51f8f93f0ded53146da upstream.

USB Gen1 requires scrambling and 8b/10b encoding to be performed in the
physical layer. Do not bypass PHY-side scrambler or encoder/decoder for
USB operation, as mandated by the USB 3.x specification.

Scrambler and 8b/10b bypass remain restricted to SATA and SGMII
modes, where encoding is handled in the controller.

Fixes: 4a33bea00314 ("phy: zynqmp: Add PHY driver for the Xilinx ZynqMP Gigabit Transceiver")
Cc: stable@vger.kernel.org
Signed-off-by: Nava kishore Manne <nava.kishore.manne@amd.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Link: https://patch.msgid.link/20260627155229.2791113-4-radhey.shyam.pandey@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/phy/xilinx/phy-zynqmp.c |   39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

--- a/drivers/phy/xilinx/phy-zynqmp.c
+++ b/drivers/phy/xilinx/phy-zynqmp.c
@@ -488,15 +488,30 @@ static void xpsgtr_lane_set_protocol(str
 	}
 }
 
-/* Bypass (de)scrambler and 8b/10b decoder and encoder. */
-static void xpsgtr_bypass_scrambler_8b10b(struct xpsgtr_phy *gtr_phy)
+/**
+ * xpsgtr_bypass_scrambler_8b10b - Configure scrambler/encoder behavior
+ * @gtr_phy: pointer to lane context
+ * @bypass: true to enable scrambler/encoder bypass (SATA/SGMII),
+ *          false to disable scrambler/encoder bypass (USB3)
+ *
+ * Uses RMW to preserve reserved and unrelated register fields.
+ */
+static void xpsgtr_bypass_scrambler_8b10b(struct xpsgtr_phy *gtr_phy,
+					  bool bypass)
 {
-	xpsgtr_clr_set_phy(gtr_phy, L0_TM_DIG_6,
-			   L0_TM_DIS_DESCRAMBLE_DECODER,
-			   L0_TM_DIS_DESCRAMBLE_DECODER);
-	xpsgtr_clr_set_phy(gtr_phy, L0_TX_DIG_61,
-			   L0_TM_DISABLE_SCRAMBLE_ENCODER,
-			   L0_TM_DISABLE_SCRAMBLE_ENCODER);
+	if (bypass) {
+		xpsgtr_clr_set_phy(gtr_phy, L0_TM_DIG_6,
+				   L0_TM_DIS_DESCRAMBLE_DECODER,
+				   L0_TM_DIS_DESCRAMBLE_DECODER);
+		xpsgtr_clr_set_phy(gtr_phy, L0_TX_DIG_61,
+				   L0_TM_DISABLE_SCRAMBLE_ENCODER,
+				   L0_TM_DISABLE_SCRAMBLE_ENCODER);
+	} else {
+		xpsgtr_clr_set_phy(gtr_phy, L0_TM_DIG_6,
+				   L0_TM_DIS_DESCRAMBLE_DECODER, 0);
+		xpsgtr_clr_set_phy(gtr_phy, L0_TX_DIG_61,
+				   L0_TM_DISABLE_SCRAMBLE_ENCODER, 0);
+	}
 }
 
 /* DP-specific initialization. */
@@ -517,7 +532,7 @@ static void xpsgtr_phy_init_sata(struct
 {
 	struct xpsgtr_dev *gtr_dev = gtr_phy->dev;
 
-	xpsgtr_bypass_scrambler_8b10b(gtr_phy);
+	xpsgtr_bypass_scrambler_8b10b(gtr_phy, true);
 
 	writel(gtr_phy->lane, gtr_dev->siou + SATA_CONTROL_OFFSET);
 }
@@ -533,7 +548,7 @@ static void xpsgtr_phy_init_sgmii(struct
 	xpsgtr_clr_set(gtr_dev, TX_PROT_BUS_WIDTH, mask, val);
 	xpsgtr_clr_set(gtr_dev, RX_PROT_BUS_WIDTH, mask, val);
 
-	xpsgtr_bypass_scrambler_8b10b(gtr_phy);
+	xpsgtr_bypass_scrambler_8b10b(gtr_phy, true);
 }
 
 /* Configure TX de-emphasis and margining for DP. */
@@ -694,6 +709,10 @@ static int xpsgtr_phy_init(struct phy *p
 	case ICM_PROTOCOL_SGMII:
 		xpsgtr_phy_init_sgmii(gtr_phy);
 		break;
+
+	case ICM_PROTOCOL_USB:
+		xpsgtr_bypass_scrambler_8b10b(gtr_phy, false);
+		break;
 	}
 
 	goto out;