realtek: pcs: derive SerDes link count from DT at probe time

Previously, sds->num_of_links was incremented from rtpcs_create() as
each DSA port bound its phylink_pcs. The count therefore relied on a
temporal contract (DSA must finish enumerating before pcs_config runs)
and on rtpcs_create() being the single chokepoint for all consumers.

Replace this with a probe-time scan of pcs-handle references in the
live OF tree: for every available consumer node carrying a pcs-handle
property pointing at one of our SerDes subnodes, bump that SerDes'
num_of_links. After the scan, the count is final regardless of when
or whether DSA later calls in.

To allow of_parse_phandle_with_args() to walk the property correctly,
add #pcs-cells = <0> to every serdes@N node in the 838x/839x/930x/931x
.dtsi files. A future cell-bearing form remains possible without
touching the scan.

Over-references (DT pointing more consumers at one SerDes than the
hardware can carry) are clamped at RTPCS_MAX_LINKS_PER_SDS and warned
about, but do not fail probe — the correctly-wired ports on that
SerDes still come up, and only the surplus reference is dropped.

The bounds check and the bare ++ in rtpcs_create() become redundant
under the scan-driven count and are removed.

This decouples num_of_links from DSA call ordering and is a prereq
for migrating to fwnode_pcs providers, where rtpcs_create() goes away
as the centralised counter.

Link: https://github.com/openwrt/openwrt/pull/23484
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>

target/linux/realtek/dts/rtl838x.dtsi

@@ -252,21 +252,27 @@
 
 			serdes0: serdes@0 {
 				reg = <0>;
+				#pcs-cells = <0>;
 			};
 			serdes1: serdes@1 {
 				reg = <1>;
+				#pcs-cells = <0>;
 			};
 			serdes2: serdes@2 {
 				reg = <2>;
+				#pcs-cells = <0>;
 			};
 			serdes3: serdes@3 {
 				reg = <3>;
+				#pcs-cells = <0>;
 			};
 			serdes4: serdes@4 {
 				reg = <4>;
+				#pcs-cells = <0>;
 			};
 			serdes5: serdes@5 {
 				reg = <5>;
+				#pcs-cells = <0>;
 			};
 		};
 

target/linux/realtek/dts/rtl839x.dtsi

@@ -265,45 +265,59 @@
 
 			serdes0: serdes@0 {
 				reg = <0>;
+				#pcs-cells = <0>;
 			};
 			serdes1: serdes@1 {
 				reg = <1>;
+				#pcs-cells = <0>;
 			};
 			serdes2: serdes@2 {
 				reg = <2>;
+				#pcs-cells = <0>;
 			};
 			serdes3: serdes@3 {
 				reg = <3>;
+				#pcs-cells = <0>;
 			};
 			serdes4: serdes@4 {
 				reg = <4>;
+				#pcs-cells = <0>;
 			};
 			serdes5: serdes@5 {
 				reg = <5>;
+				#pcs-cells = <0>;
 			};
 			serdes6: serdes@6 {
 				reg = <6>;
+				#pcs-cells = <0>;
 			};
 			serdes7: serdes@7 {
 				reg = <7>;
+				#pcs-cells = <0>;
 			};
 			serdes8: serdes@8 {
 				reg = <8>;
+				#pcs-cells = <0>;
 			};
 			serdes9: serdes@9 {
 				reg = <9>;
+				#pcs-cells = <0>;
 			};
 			serdes10: serdes@10 {
 				reg = <10>;
+				#pcs-cells = <0>;
 			};
 			serdes11: serdes@11 {
 				reg = <11>;
+				#pcs-cells = <0>;
 			};
 			serdes12: serdes@12 {
 				reg = <12>;
+				#pcs-cells = <0>;
 			};
 			serdes13: serdes@13 {
 				reg = <13>;
+				#pcs-cells = <0>;
 			};
 		};
 

target/linux/realtek/dts/rtl930x.dtsi

@@ -252,39 +252,51 @@
 
 			serdes0: serdes@0 {
 				reg = <0>;
+				#pcs-cells = <0>;
 			};
 			serdes1: serdes@1 {
 				reg = <1>;
+				#pcs-cells = <0>;
 			};
 			serdes2: serdes@2 {
 				reg = <2>;
+				#pcs-cells = <0>;
 			};
 			serdes3: serdes@3 {
 				reg = <3>;
+				#pcs-cells = <0>;
 			};
 			serdes4: serdes@4 {
 				reg = <4>;
+				#pcs-cells = <0>;
 			};
 			serdes5: serdes@5 {
 				reg = <5>;
+				#pcs-cells = <0>;
 			};
 			serdes6: serdes@6 {
 				reg = <6>;
+				#pcs-cells = <0>;
 			};
 			serdes7: serdes@7 {
 				reg = <7>;
+				#pcs-cells = <0>;
 			};
 			serdes8: serdes@8 {
 				reg = <8>;
+				#pcs-cells = <0>;
 			};
 			serdes9: serdes@9 {
 				reg = <9>;
+				#pcs-cells = <0>;
 			};
 			serdes10: serdes@10 {
 				reg = <10>;
+				#pcs-cells = <0>;
 			};
 			serdes11: serdes@11 {
 				reg = <11>;
+				#pcs-cells = <0>;
 			};
 		};
 

target/linux/realtek/dts/rtl931x.dtsi

@@ -284,45 +284,59 @@
 
 			serdes0: serdes@0 {
 				reg = <0>;
+				#pcs-cells = <0>;
 			};
 			serdes1: serdes@1 {
 				reg = <1>;
+				#pcs-cells = <0>;
 			};
 			serdes2: serdes@2 {
 				reg = <2>;
+				#pcs-cells = <0>;
 			};
 			serdes3: serdes@3 {
 				reg = <3>;
+				#pcs-cells = <0>;
 			};
 			serdes4: serdes@4 {
 				reg = <4>;
+				#pcs-cells = <0>;
 			};
 			serdes5: serdes@5 {
 				reg = <5>;
+				#pcs-cells = <0>;
 			};
 			serdes6: serdes@6 {
 				reg = <6>;
+				#pcs-cells = <0>;
 			};
 			serdes7: serdes@7 {
 				reg = <7>;
+				#pcs-cells = <0>;
 			};
 			serdes8: serdes@8 {
 				reg = <8>;
+				#pcs-cells = <0>;
 			};
 			serdes9: serdes@9 {
 				reg = <9>;
+				#pcs-cells = <0>;
 			};
 			serdes10: serdes@10 {
 				reg = <10>;
+				#pcs-cells = <0>;
 			};
 			serdes11: serdes@11 {
 				reg = <11>;
+				#pcs-cells = <0>;
 			};
 			serdes12: serdes@12 {
 				reg = <12>;
+				#pcs-cells = <0>;
 			};
 			serdes13: serdes@13 {
 				reg = <13>;
+				#pcs-cells = <0>;
 			};
 		};
 

target/linux/realtek/files-6.18/drivers/net/pcs/pcs-rtl-otto.c

@@ -4107,8 +4107,6 @@ struct phylink_pcs *rtpcs_create(struct device *dev, struct device_node *np, int
 	sds = &ctrl->serdes[sds_id];
 	if (rtpcs_sds_read(sds, 0, 0) < 0)
 		return ERR_PTR(-EINVAL);
-	if (sds->num_of_links >= RTPCS_MAX_LINKS_PER_SDS)
-		return ERR_PTR(-ERANGE);
 
 	link = devm_kzalloc(ctrl->dev, sizeof(*link), GFP_KERNEL);
 	if (!link) {
@@ -4118,7 +4116,6 @@ struct phylink_pcs *rtpcs_create(struct device *dev, struct device_node *np, int
 
 	device_link_add(dev, ctrl->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
 
-	sds->num_of_links++;
 	link->ctrl = ctrl;
 	link->port = port;
 	link->sds = sds;
@@ -4166,6 +4163,41 @@ static void rtpcs_sds_put_of_node(void *data)
 	of_node_put(sds->of_node);
 }
 
+static void rtpcs_count_links(struct rtpcs_ctrl *ctrl)
+{
+	struct device_node *consumer __free(device_node) = NULL;
+	struct of_phandle_args args;
+
+	for_each_node_with_property(consumer, "pcs-handle") {
+		int idx = 0;
+
+		if (!of_device_is_available(consumer))
+			continue;
+
+		while (!of_parse_phandle_with_args(consumer, "pcs-handle",
+						   "#pcs-cells", idx++, &args)) {
+			struct device_node *arg_np __free(device_node) = args.np;
+
+			for (int s = 0; s < ctrl->cfg->serdes_count; s++) {
+				struct rtpcs_serdes *sds = &ctrl->serdes[s];
+
+				if (arg_np != sds->of_node)
+					continue;
+
+				if (sds->num_of_links >= RTPCS_MAX_LINKS_PER_SDS) {
+					dev_warn(ctrl->dev,
+						 "%pOF: pcs-handle to sds%u exceeds max %u, clamping\n",
+						 consumer, sds->id, RTPCS_MAX_LINKS_PER_SDS);
+					break;
+				}
+
+				sds->num_of_links++;
+				break;
+			}
+		}
+	}
+}
+
 static int rtpcs_probe(struct platform_device *pdev)
 {
 	struct device_node *np = pdev->dev.of_node;
@@ -4220,6 +4252,8 @@ static int rtpcs_probe(struct platform_device *pdev)
 			return ret;
 	}
 
+	rtpcs_count_links(ctrl);
+
 	if (ctrl->cfg->init) {
 		ret = ctrl->cfg->init(ctrl);
 		if (ret)