fix: address PR review feedback for MIDI 2.0 drivers

Host driver (midi2_host.c):
- midih2_open() now returns actual parsed length instead of max_len,
  preventing composite device interface conflicts
- Parsers (alt0/alt1) refactored to return const uint8_t* end pointer
  following midi_host.c switch/case pattern
- Alt 1 CS Endpoint now parses MIDI 2.0 layout (bNumGrpTrmBlk at
  offset 3 with MIDI_CS_ENDPOINT_GENERAL_2_0 subtype check) instead
  of reusing MIDI 1.0 struct (bNumEmbMIDIJack)
- midih2_set_config() now issues SET_INTERFACE control request via
  tuh_interface_set() before completing configuration. Falls back to
  alt 0 if SET_INTERFACE fails
- Extracted midih2_set_config_complete() and midih2_set_interface_cb()
  for async SET_INTERFACE handling

Device driver (midi2_device.c):
- midi2d_open() skip loop now checks bInterfaceNumber, stopping at
  interfaces that belong to other functions in composite devices
- SET_INTERFACE handler now rejects alt > 1 (returns false/stall)
- Named constants for GTB descriptor types and MIDI protocol values

Descriptor macros (usbd.h):
- TUD_MIDI2_DESC_ALT1_HEAD: iInterface set to 0 (consistent with
  Alt 0), wTotalLength now uses TUD_MIDI2_DESC_ALT1_CS_LEN to cover
  all Alt 1 class-specific descriptors
- TUD_MIDI2_DESC_ALT1_EP: now accepts GTB ID list via variadic args,
  emitting complete CS endpoint descriptor

Host example:
- CMakeLists.txt restricted to rp2040 family (display.c requires
  Pico SDK headers)
- display.c: null terminator after strncpy in log scroll

Documentation:
- class_drivers.rst updated to reflect SET_INTERFACE behavior and
  auto-select with fallback

Addresses: Codex P1 (#1, #2, #3), Copilot (#4-#9)

1 files changed, 12 insertions, 2 deletions

diff --git a/src/class/midi/midi2_device.c b/src/class/midi/midi2_device.c
index 9363aac11..aecbda4c5 100644
--- a/src/class/midi/midi2_device.c
+++ b/src/class/midi/midi2_device.c
@@ -505,12 +505,19 @@ uint16_t midi2d_open(uint8_t rhport, const tusb_desc_interface_t* desc_itf, uint
   }
 
   // Skip remaining descriptors (alt setting 1, CS endpoints, GTB)
+  // Stop at any interface descriptor that is not our MIDI Streaming alt setting
   while (tu_desc_in_bounds(p_desc, desc_end)) {
     uint8_t dtype = tu_desc_type(p_desc);
-    if (dtype != TUSB_DESC_CS_INTERFACE && dtype != TUSB_DESC_CS_ENDPOINT &&
-        dtype != TUSB_DESC_INTERFACE && dtype != TUSB_DESC_ENDPOINT) {
+
+    if (dtype == TUSB_DESC_INTERFACE) {
+      const tusb_desc_interface_t* next_itf = (const tusb_desc_interface_t*) p_desc;
+      // Continue only if this is an alternate setting of our own interface
+      if (next_itf->bInterfaceNumber != desc_midi->bInterfaceNumber) break;
+    } else if (dtype != TUSB_DESC_CS_INTERFACE && dtype != TUSB_DESC_CS_ENDPOINT &&
+               dtype != TUSB_DESC_ENDPOINT) {
       break;
     }
+
     p_desc = tu_desc_next(p_desc);
   }
 
@@ -528,6 +535,9 @@ bool midi2d_control_xfer_cb(uint8_t rhport, uint8_t stage, const tusb_control_re
       uint8_t itf_num = tu_u16_low(request->wIndex);
       uint8_t alt     = tu_u16_low(request->wValue);
 
+      // Only Alt Setting 0 (MIDI 1.0) and 1 (UMP) are valid
+      if (alt > 1) return false;
+
       uint8_t idx = find_midi2_itf_by_num(itf_num);
       if (idx >= CFG_TUD_MIDI2) return false;