Date: Wed, 21 Feb 2024 00:34:42 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Madalin Bucur <madalin.bucur@....com>,
	Sean Anderson <sean.anderson@...o.com>,
	Russell King <linux@...linux.org.uk>,
	Zachary Goldstein <zachary.goldstein@...current-rt.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH net] net: dpaa: fman_memac: accept phy-interface-type = "10gbase-r" in the device tree

Since commit 5d93cfcf7360 ("net: dpaa: Convert to phylink"), we support
the "10gbase-r" phy-mode through a driver-based conversion of "xgmii",
but we still don't actually support it when the device tree specifies
"10gbase-r" proper.

This is because boards such as LS1046A-RDB do not define pcs-handle-names
(for whatever reason) in the ethernet@...00 device tree node, and the
code enters through this code path:

	err = of_property_match_string(mac_node, "pcs-handle-names", "xfi");
	// code takes neither branch and falls through
	if (err >= 0) {
		(...)
	} else if (err != -EINVAL && err != -ENODATA) {
		goto _return_fm_mac_free;
	}

	(...)

	/* For compatibility, if pcs-handle-names is missing, we assume this
	 * phy is the first one in pcsphy-handle
	 */
	err = of_property_match_string(mac_node, "pcs-handle-names", "sgmii");
	if (err == -EINVAL || err == -ENODATA)
		pcs = memac_pcs_create(mac_node, 0); // code takes this branch
	else if (err < 0)
		goto _return_fm_mac_free;
	else
		pcs = memac_pcs_create(mac_node, err);

	// A default PCS is created and saved in "pcs"

	// This determination fails and mistakenly saves the default PCS
	// memac->sgmii_pcs instead of memac->xfi_pcs, because at this
	// stage, mac_dev->phy_if == PHY_INTERFACE_MODE_10GBASER.
	if (err && mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
		memac->xfi_pcs = pcs;
	else
		memac->sgmii_pcs = pcs;

In other words, in the absence of pcs-handle-names, the default
xfi_pcs assignment logic only works when in the device tree we have
PHY_INTERFACE_MODE_XGMII.

By reversing the order between the fallback xfi_pcs assignment and the
"xgmii" overwrite with "10gbase-r", we are able to support both values
in the device tree, with identical behavior.

Currently, it is impossible to make the s/xgmii/10gbase-r/ device tree
conversion, because it would break forward compatibility (new device
tree with old kernel). The only way to modify existing device trees to
phy-interface-mode = "10gbase-r" is to fix stable kernels to accept this
value and handle it properly.

One reason why the conversion is desirable is because with pre-phylink
kernels, the Aquantia PHY driver used to warn about the improper use
of PHY_INTERFACE_MODE_XGMII [1]. It is best to have a single (latest)
device tree that works with all supported stable kernel versions.

Note that the blamed commit does not constitute a regression per se.
Older stable kernels like 6.1 still do not work with "10gbase-r", but
for a different reason. That is a battle for another time.

[1] https://lore.kernel.org/netdev/20240214-ls1046-dts-use-10gbase-r-v1-1-8c2d68547393@concurrent-rt.com/

Fixes: 5d93cfcf7360 ("net: dpaa: Convert to phylink")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 .../net/ethernet/freescale/fman/fman_memac.c   | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fman/fman_memac.c b/drivers/net/ethernet/freescale/fman/fman_memac.c
index e30bf75b1d48..0996759907a8 100644
--- a/drivers/net/ethernet/freescale/fman/fman_memac.c
+++ b/drivers/net/ethernet/freescale/fman/fman_memac.c
@@ -1076,6 +1076,14 @@ int memac_initialization(struct mac_device *mac_dev,
 	unsigned long		 capabilities;
 	unsigned long		*supported;
 
+	/* The internal connection to the serdes is XGMII, but this isn't
+	 * really correct for the phy mode (which is the external connection).
+	 * However, this is how all older device trees say that they want
+	 * 10GBASE-R (aka XFI), so just convert it for them.
+	 */
+	if (mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
+		mac_dev->phy_if = PHY_INTERFACE_MODE_10GBASER;
+
 	mac_dev->phylink_ops		= &memac_mac_ops;
 	mac_dev->set_promisc		= memac_set_promiscuous;
 	mac_dev->change_addr		= memac_modify_mac_address;
@@ -1142,7 +1150,7 @@ int memac_initialization(struct mac_device *mac_dev,
 	 * (and therefore that xfi_pcs cannot be set). If we are defaulting to
 	 * XGMII, assume this is for XFI. Otherwise, assume it is for SGMII.
 	 */
-	if (err && mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
+	if (err && mac_dev->phy_if == PHY_INTERFACE_MODE_10GBASER)
 		memac->xfi_pcs = pcs;
 	else
 		memac->sgmii_pcs = pcs;
@@ -1156,14 +1164,6 @@ int memac_initialization(struct mac_device *mac_dev,
 		goto _return_fm_mac_free;
 	}
 
-	/* The internal connection to the serdes is XGMII, but this isn't
-	 * really correct for the phy mode (which is the external connection).
-	 * However, this is how all older device trees say that they want
-	 * 10GBASE-R (aka XFI), so just convert it for them.
-	 */
-	if (mac_dev->phy_if == PHY_INTERFACE_MODE_XGMII)
-		mac_dev->phy_if = PHY_INTERFACE_MODE_10GBASER;
-
 	/* TODO: The following interface modes are supported by (some) hardware
 	 * but not by this driver:
 	 * - 1000BASE-KX
-- 
2.34.1

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