[PATCH net-next v4 2/2] net: pcs: xpcs: make supported_interfaces authoritative

[Coia Prant <coiaprant@gmail.com>]

pcs.supported_interfaces is the mask of interfaces a given xpcs
instance actually supports. The compat table describes what the
Synopsys IP can do in general, but a specific integration may support
a different subset. For example, the RK3568 XPCS supports 1000BASE-X,
SGMII and QSGMII in hardware, but does not implement the C73,
10GBASE-R or 2500BASE-X modes that the Synopsys compat table
advertises.

However, xpcs_find_compat() only walks desc->compat[] and does not look
at pcs.supported_interfaces. If a caller ever passes an interface
outside the mask, the core would still find and configure a compat
entry for it, contradicting the mask the glue already set. This was a
known gap: the mask was written but never consulted by the core.

Fix both sides:

- In xpcs_find_compat(), return NULL when the interface is not in
  pcs.supported_interfaces, so the mask is authoritative for what the
  core will configure.
- In the Rockchip glue, build a platform mask with the three modes
  supported by RK3568 (1000BASE-X, SGMII, QSGMII) and intersect it
  with the core's supported_interfaces using phy_interface_and().
  This narrows the mask inherited from the generic compat table so it
  reflects the actual SoC capabilities.

Note that QSGMII is currently filtered out (a no-op) because the core's
compat table does not support it yet, which demonstrates the intended
filtering behavior of this intersection. If the core adds QSGMII
support in the future, the glue will automatically pick it up.

This is a logical inconsistency rather than a user-visible bug in a
released kernel: the affected Rockchip platform is not present in any
released version, and the MAC side forces the phy mode, so phylink does
not normally pass an interface outside the mask. The patch makes the
mask the single source of truth for both the core and the glue.

Signed-off-by: Coia Prant <coiaprant@gmail.com>
---
 drivers/net/pcs/pcs-xpcs-rk.c | 10 ++++++++++
 drivers/net/pcs/pcs-xpcs.c    |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/drivers/net/pcs/pcs-xpcs-rk.c b/drivers/net/pcs/pcs-xpcs-rk.c
index ad187fba4e9d..e29f473776b2 100644
--- a/drivers/net/pcs/pcs-xpcs-rk.c
+++ b/drivers/net/pcs/pcs-xpcs-rk.c
@@ -480,6 +480,7 @@ MODULE_DEVICE_TABLE(of, xpcs_rk_of_ids);
 
 struct dw_xpcs *xpcs_rk_create(struct device *dev, struct device_node *pcs, int port)
 {
+	DECLARE_PHY_INTERFACE_MASK_ZERO(supported_interfaces);
 	struct platform_device *pdev;
 	struct dw_xpcs_rk *pxpcs;
 	struct dw_xpcs *xpcs;
@@ -536,6 +537,15 @@ struct dw_xpcs *xpcs_rk_create(struct device *dev, struct device_node *pcs, int
 		return xpcs;
 	}
 
+	/*
+	 * The RK3568 XPCS supports 1000BASE-X, SGMII and QSGMII.
+	 */
+	__set_bit(PHY_INTERFACE_MODE_1000BASEX, supported_interfaces);
+	__set_bit(PHY_INTERFACE_MODE_SGMII, supported_interfaces);
+	__set_bit(PHY_INTERFACE_MODE_QSGMII, supported_interfaces);
+	phy_interface_and(xpcs->pcs.supported_interfaces, xpcs->pcs.supported_interfaces,
+			  supported_interfaces);
+
 	xpcs_config_eee_mult_fact(xpcs, pxpcs->eee_mult_fact);
 	put_device(&pdev->dev);
 	return xpcs;
diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index 6466e0ff2a98..46878a66064e 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -169,6 +169,9 @@ xpcs_find_compat(struct dw_xpcs *xpcs, phy_interface_t interface)
 {
 	const struct dw_xpcs_compat *compat;
 
+	if (!test_bit(interface, xpcs->pcs.supported_interfaces))
+		return NULL;
+
 	for (compat = xpcs->desc->compat; compat->supported; compat++)
 		if (compat->interface == interface)
 			return compat;
-- 
2.47.3