core: dt_driver: do not defer probe on skip phandler arguments

Prevent dt_driver_device_from_node_idx_prop() to request driver probe
deferral when needing to skip phandle arguments cells related to
providers not yet registered. When skipping these phandle argument cells
we don't really need the skipped provider is registered, we can read
the #xxx-cells property in the provider DT node straight.

For example, consider a driver which DT node defines:
  clocks = <&foo_clock 1 2 3>, <&bar_clock 2>;
  clock-names = "foo", "bar";
If driver calls clk_get_by_name(fdt, node, "bar"), it does not need to
wait &foo_clock related driver to be already probed, it does not even
need the driver to be ever probed.

Fixes: a22e85b ("core: dt_driver: factorize clk_dt_get_from_provider()")
Signed-off-by: Etienne Carriere <[email protected]>

core/kernel/dt_driver.c

@@ -383,21 +383,45 @@ TEE_Result dt_driver_device_from_node_idx_prop(const char *prop_name,
 				return TEE_ERROR_GENERIC;
 
 			prv = dt_driver_get_provider_by_node(nodeoffset, type);
-			if (!prv)
-				return TEE_ERROR_DEFER_DRIVER_INIT;
 		} else {
 			prv = dt_driver_get_provider_by_phandle(phandle, type);
-			if (!prv)
-				return TEE_ERROR_DEFER_DRIVER_INIT;
 		}
 
-		prv_cells = dt_driver_provider_cells(prv);
+		if (prv) {
+			prv_cells = dt_driver_provider_cells(prv);
+		} else if (prop_idx) {
+			/*
+			 * When we need to skip another provider phandle
+			 * arguments cells (aka when prop_idx != 0), we don't
+			 * really need the skipped provider to be already
+			 * registered, we can look straight in its DT node.
+			 */
+			phandle_node = fdt_node_offset_by_phandle(fdt, phandle);
+			if (phandle_node < 0) {
+				DMSG("Can't find node for phandle %"PRIu32,
+				     phandle);
+				return TEE_ERROR_GENERIC;
+			}
+
+			prv_cells = fdt_get_dt_driver_cells(fdt, phandle_node,
+							    type);
+			if (prv_cells < 0) {
+				DMSG("Can't find cells count on node %s: %d",
+				     fdt_get_name(fdt, phandle_node, NULL),
+				     prv_cells);
+				return TEE_ERROR_GENERIC;
+			}
+		}
+
 		if (prop_idx) {
 			prop_idx--;
 			idx += sizeof(phandle) + prv_cells * sizeof(uint32_t);
 			continue;
 		}
 
+		if (!prv)
+			return TEE_ERROR_DEFER_DRIVER_INIT;
+
 		/* Skip property cell with the phandle, already handled */
 		idx32++;