From d9fa3835bb8913757c74af96fa8db0d621e2e980 Mon Sep 17 00:00:00 2001
From: Jonas Gorski <jonas.gorski@gmail.com>
Date: Mon, 9 Jun 2025 11:18:24 +0200
Subject: [PATCH] net: dsa: b53: bcm531x5: fix cpu rgmii mode interpretation
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b53_adjust_531x5_rgmii() incorrectly enable delays in rgmii mode, but
disables them in rgmii-id mode. Only rgmii-txid is correctly handled.

Fix this by correctly enabling rx delay in rgmii-rxid and rgmii-id
modes, and tx delay in rgmii-txid and rgmii-id modes.

Since b53_adjust_531x5_rgmii() is only called for fixed-link ports,
these are usually used as the CPU port, connected to a MAC. This means
the chip is assuming the role of the PHY and enabling delays is
expected.

Since this has the potential to break existing setups, add a config
options to treat rgmii as rgmii-id, and enable it by default.

I only made the quirk fixup rgmii to rgmii-id, but not rgmii-id to
rgmii, or no delays for rgmii-rxid. My reasoning is that

a) Boards not requiring internal delays are probably rather seldom, so I
   considered the likelyhood requiring/wrongly specifying rgmii-id when
   they need rgmii as very unlikely.
   And if they understand the difference enough to know to use the
   "wrong" mode, they would have hopefully noticed the discrepancy and
   reported the issue by now.
b) I don't want to require new users to wrongly use rgmii to get
   rgmii-id behavior with the quirk enabled.

Fixes: 967dd82ffc52 ("net: dsa: b53: Add support for Broadcom RoboSwitch")
Reported-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
---
 drivers/net/dsa/b53/Kconfig      | 10 ++++++++++
 drivers/net/dsa/b53/b53_common.c | 33 +++++++++++++++++++++++---------
 2 files changed, 34 insertions(+), 9 deletions(-)

--- a/drivers/net/dsa/b53/Kconfig
+++ b/drivers/net/dsa/b53/Kconfig
@@ -47,3 +47,13 @@ config B53_SERDES
 	default ARCH_BCM_NSP
 	help
 	  Select to enable support for SerDes on e.g: Northstar Plus SoCs.
+
+config B53_QUIRK_IMP_RGMII_IMPLIES_DELAYS
+	bool "Treat RGMII as RGMII-ID for CPU port"
+	depends on B53
+	default y
+	help
+	  Select to enable RGMII delays also in RGMII (no ID) mode for the CPU
+	  port to mirror old driver behavior.
+	  Enable this if your board wrongly uses RGMII instead of RGMII-ID as
+	  the phy interface, but actually requires internal delays enabled.
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -1444,6 +1444,16 @@ static void b53_adjust_531x5_rgmii(struc
 	else
 		off = B53_RGMII_CTRL_P(port);
 
+	if (IS_ENABLED(CONFIG_B53_QUIRK_IMP_RGMII_IMPLIES_DELAYS) &&
+	    interface == PHY_INTERFACE_MODE_RGMII) {
+		/* Older driver versions incorrectly applied delays in
+		 * PHY_INTERFACE_MODE_RGMII mode.
+		 *
+		 * So fixup the interface to match the old behavior.
+		 */
+		interface = PHY_INTERFACE_MODE_RGMII_ID;
+	}
+
 	/* Configure the port RGMII clock delay by DLL disabled and
 	 * tx_clk aligned timing (restoring to reset defaults)
 	 */
@@ -1455,19 +1465,24 @@ static void b53_adjust_531x5_rgmii(struc
 	 * account for this internal delay that is inserted, otherwise
 	 * the switch won't be able to receive correctly.
 	 *
+	 * PHY_INTERFACE_MODE_RGMII_RXID means RX internal delay, make
+	 * sure that we enable the port RX clock internal sampling delay
+	 * to account for this internal delay that is inserted, otherwise
+	 * the switch won't be able to send correctly.
+	 *
+	 * PHY_INTERFACE_MODE_RGMII_ID means both RX and TX internal delay,
+	 * make sure that we enable delays for both.
+	 *
 	 * PHY_INTERFACE_MODE_RGMII means that we are not introducing
 	 * any delay neither on transmission nor reception, so the
-	 * BCM53125 must also be configured accordingly to account for
-	 * the lack of delay and introduce
-	 *
-	 * The BCM53125 switch has its RX clock and TX clock control
-	 * swapped, hence the reason why we modify the TX clock path in
-	 * the "RGMII" case
+	 * BCM53125 must also be configured accordingly.
 	 */
-	if (interface == PHY_INTERFACE_MODE_RGMII_TXID)
+	if (interface == PHY_INTERFACE_MODE_RGMII_TXID ||
+	    interface == PHY_INTERFACE_MODE_RGMII_ID)
 		rgmii_ctrl |= RGMII_CTRL_DLL_TXC;
-	if (interface == PHY_INTERFACE_MODE_RGMII)
-		rgmii_ctrl |= RGMII_CTRL_DLL_TXC | RGMII_CTRL_DLL_RXC;
+	if (interface == PHY_INTERFACE_MODE_RGMII_RXID ||
+	    interface == PHY_INTERFACE_MODE_RGMII_ID)
+		rgmii_ctrl |= RGMII_CTRL_DLL_RXC;
 
 	if (dev->chip_id != BCM53115_DEVICE_ID)
 		rgmii_ctrl |= RGMII_CTRL_TIMING_SEL;
