usb: readable PORTSC decode, link-state names, and device string descriptors

Make the USB diagnostic logs scannable by eye:
- usb-ids gains speedName + linkStateName (USB3 PORTSC link states: U0,
  RxDetect, Polling, ...), host-tested with usb-ids.
- The PORTSC dump decodes the register instead of printing hex flags:
    PORTSC[3] 0x00021203: connected, enabled, link=U0, power=on, SuperSpeed
    PORTSC[5] 0x00020ee1: connected, disabled, link=Polling, power=on, High-speed
  (the raw word stays for reference). A USB2 device reads connected+
  disabled+Polling until reset — so the user's next log shows at a glance
  whether the companion port ever reaches that state.
- The library reads STRING descriptors (readString, UTF-16LE -> ASCII,
  English langid), and the device line now names the maker + product:
    port 5 device: Hub "Genesys Logic USB3.0 Hub" (0x05e3:0x0626), 1 interface(s)
  instead of a bare vendor/product id pair.

Full USB case set green (hub regexes follow the new 'device: <class>
"<maker> <product>"' format). Branch diagnostics for the SuperSpeed
compound-hub investigation.

system/devices/usb-ids.zig

@@ -103,6 +103,38 @@ pub fn className(class: u8) []const u8 {
     };
 }
 
+/// The USB speed class (as xHCI reports it in PORTSC/slot contexts) named.
+pub fn speedName(speed: u32) []const u8 {
+    return switch (speed) {
+        1 => "Full-speed",
+        2 => "Low-speed",
+        3 => "High-speed",
+        4 => "SuperSpeed",
+        5 => "SuperSpeedPlus",
+        else => "unknown-speed",
+    };
+}
+
+/// A USB3 Port Link State (xHCI PORTSC PLS field) named.
+pub fn linkStateName(pls: u32) []const u8 {
+    return switch (pls) {
+        0 => "U0",
+        1 => "U1",
+        2 => "U2",
+        3 => "U3-suspended",
+        4 => "Disabled",
+        5 => "RxDetect",
+        6 => "Inactive",
+        7 => "Polling",
+        8 => "Recovery",
+        9 => "HotReset",
+        10 => "Compliance",
+        11 => "Test",
+        15 => "Resume",
+        else => "reserved",
+    };
+}
+
 /// A fuller name for a HID interface's (subclass, protocol): "HID boot keyboard"
 /// / "HID boot mouse", else just the class name. Used to make input devices
 /// recognizable in logs.

system/drivers/usb-xhci-bus/usb-xhci-bus.zig

@@ -230,9 +230,15 @@ fn bringUpPort(manager: runtime.ipc.Handle, engine: *library.Controller, port: u
         std.log.info("port {d} enumeration failed", .{port});
         return;
     }
-    std.log.info("port {d} device: {s} vendor 0x{x:0>4} product 0x{x:0>4}, {d} interface(s)", .{
+    var maker_buffer: [64]u8 = undefined;
+    var product_buffer: [64]u8 = undefined;
+    const maker = engine.readString(usb_device, @intFromEnum(usb_device.device_descriptor.manufacturer_index), &maker_buffer) orelse "?";
+    const product = engine.readString(usb_device, @intFromEnum(usb_device.device_descriptor.product_index), &product_buffer) orelse "?";
+    std.log.info("port {d} device: {s} \"{s} {s}\" (0x{x:0>4}:0x{x:0>4}), {d} interface(s)", .{
         port,
         usb_ids.className(usb_device.device_descriptor.device_class),
+        maker,
+        product,
         usb_device.device_descriptor.vendor_id,
         usb_device.device_descriptor.product_id,
         usb_device.interface_count,
@@ -280,9 +286,15 @@ fn bringUpBehindHub(manager: runtime.ipc.Handle, engine: *library.Controller, hu
         std.log.info("hub slot {d} port {d}: enumeration failed", .{ hub.slot_id, port });
         return;
     }
-    std.log.info("hub slot {d} port {d} device: {s} vendor 0x{x:0>4} product 0x{x:0>4}, {d} interface(s)", .{
+    var maker_buffer: [64]u8 = undefined;
+    var product_buffer: [64]u8 = undefined;
+    const maker = engine.readString(usb_device, @intFromEnum(usb_device.device_descriptor.manufacturer_index), &maker_buffer) orelse "?";
+    const product = engine.readString(usb_device, @intFromEnum(usb_device.device_descriptor.product_index), &product_buffer) orelse "?";
+    std.log.info("hub slot {d} port {d} device: {s} \"{s} {s}\" (0x{x:0>4}:0x{x:0>4}), {d} interface(s)", .{
         hub.slot_id, port,
         usb_ids.className(usb_device.device_descriptor.device_class),
+        maker,
+        product,
         usb_device.device_descriptor.vendor_id,
         usb_device.device_descriptor.product_id,
         usb_device.interface_count,

system/drivers/usb-xhci-bus/usb-xhci-library.zig

@@ -22,6 +22,7 @@ const std = @import("std");
 const runtime = @import("runtime");
 const mmio = @import("mmio");
 const usb_abi = @import("usb-abi");
+const usb_ids = @import("usb-ids");
 const dma = runtime.dma;
 const system = runtime.system;
 
@@ -511,12 +512,46 @@ pub const Controller = struct {
         var port: u32 = 1;
         while (port <= self.max_ports) : (port += 1) {
             const portsc = self.portStatus(port);
-            std.log.info("PORTSC[{d}] = 0x{x:0>8} ccs={d} ped={d} pls={d} pp={d} speed={d}", .{
-                port, portsc, portsc & 1, (portsc >> 1) & 1, (portsc >> 5) & 0xF, (portsc >> 9) & 1, (portsc >> 10) & 0xF,
+            std.log.info("PORTSC[{d}] 0x{x:0>8}: {s}, {s}, link={s}, power={s}, {s}", .{
+                port,
+                portsc,
+                if (portsc & 1 != 0) "connected" else "empty",
+                if (portsc & 2 != 0) "enabled" else "disabled",
+                usb_ids.linkStateName((portsc >> 5) & 0xF),
+                if (portsc & (1 << 9) != 0) "on" else "off",
+                usb_ids.speedName((portsc >> 10) & 0xF),
             });
         }
     }
 
+    /// Read USB STRING descriptor `index` (English, langid 0x0409) into `out` as
+    /// ASCII, returning the slice — for logging manufacturer/product names.
+    /// Null for index 0 (no string) or a failed transfer. Non-ASCII code units
+    /// become '?'.
+    pub fn readString(self: *Controller, device: *Device, index: u8, out: []u8) ?[]const u8 {
+        if (index == 0) return null;
+        var raw: [256]u8 = undefined;
+        const request = usb_abi.Request{
+            .request_type = .{ .recipient = .device, .kind = .standard, .direction = .device_to_host },
+            .request_code = .get_descriptor,
+            .value = (@as(u16, 3) << 8) | index, // STRING descriptor
+            .index = 0x0409, // English (US)
+            .length = raw.len,
+        };
+        if (!self.controlTransfer(device, request, raw[0..], true)) return null;
+        const length = raw[0]; // bLength; the UTF-16LE payload is bytes 2..length
+        if (length < 2) return null;
+        const chars = (@min(length, raw.len) - 2) / 2;
+        var n: usize = 0;
+        var i: usize = 0;
+        while (i < chars and n < out.len) : (i += 1) {
+            const unit = @as(u16, raw[2 + i * 2]) | (@as(u16, raw[2 + i * 2 + 1]) << 8);
+            out[n] = if (unit >= 0x20 and unit < 0x7F) @intCast(unit) else '?';
+            n += 1;
+        }
+        return out[0..n];
+    }
+
     pub fn portStatus(self: *const Controller, port: u32) u32 {
         return read32(self.op_base + op_portsc_base + op_portsc_stride * (port - 1));
     }