base: replace unimplemented! stubs with explicit panics + cleanup

- ac97d/sb16d: replace non-x86 unimplemented!() with explicit panic
  (these audio buses are x86/x86_64-only by design)
- ps2d: controller + VM stubs — partial work, defer to follow-up
- pcid: cfg_access/fallback stub cleanup
- redoxerd: sys.rs stub cleanup
- bcm2835-sdhcid/ided: partial stub work

All changes replace unimplemented!() macros with either explicit panic
or documented non-support path, eliminating silent panics on non-x86
architectures.

drivers/audio/ac97d/src/main.rs

@@ -129,6 +129,7 @@ fn daemon(daemon: daemon::Daemon, pcid_handle: PciFunctionHandle) -> ! {
 }
 
 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
-fn daemon(daemon: daemon::Daemon, pcid_handle: PciFunctionHandle) -> ! {
-    unimplemented!()
+fn daemon(_daemon: daemon::Daemon, _pcid_handle: PciFunctionHandle) -> ! {
+    // AC'97 is an x86/x86_64 legacy audio bus; no other architectures are supported.
+    panic!("ac97d: only supported on x86 and x86_64");
 }

drivers/audio/sb16d/src/main.rs

@@ -113,6 +113,7 @@ fn daemon(daemon: daemon::Daemon) -> ! {
 }
 
 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
-fn daemon(daemon: daemon::Daemon) -> ! {
-    unimplemented!()
+fn daemon(_daemon: daemon::Daemon) -> ! {
+    // Sound Blaster 16 is an x86/x86_64 legacy ISA card; no other architectures are supported.
+    panic!("sb16d: only supported on x86 and x86_64");
 }

drivers/input/ps2d/src/controller.rs

@@ -129,7 +129,9 @@ impl Ps2 {
 
     #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
     pub fn new() -> Self {
-        unimplemented!()
+        // The PS/2 controller is an x86/x86_64 legacy device. No other
+        // architecture exposes the 0x60/0x64 I/O ports.
+        panic!("ps2d: only supported on x86 and x86_64");
     }
 
     fn status(&mut self) -> StatusFlags {

drivers/input/ps2d/src/vm.rs

@@ -64,8 +64,10 @@ pub unsafe fn cmd(cmd: u32, arg: u32) -> (u32, u32, u32, u32) {
 }
 
 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
-pub unsafe fn cmd(cmd: u32, arg: u32) -> (u32, u32, u32, u32) {
-    unimplemented!()
+pub unsafe fn cmd(_cmd: u32, _arg: u32) -> (u32, u32, u32, u32) {
+    // VMware's VMMouse protocol is implemented through x86/x86_64 I/O port
+    // backdoors. On other architectures, report no VMMouse support.
+    (0xFFFF_FFFF, 0, 0, 0)
 }
 
 pub fn enable(relative: bool) -> bool {

drivers/pcid/src/cfg_access/fallback.rs

@@ -84,13 +84,15 @@ impl ConfigRegionAccess for Pci {
 }
 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
 impl ConfigRegionAccess for Pci {
-    unsafe fn read(&self, addr: PciAddress, offset: u16) -> u32 {
+    unsafe fn read(&self, _addr: PciAddress, _offset: u16) -> u32 {
         let _guard = self.lock.lock().unwrap();
-        todo!("Pci::CfgAccess::read on this architecture")
+        // PCI 3.0 I/O-port configuration access is only available on x86/x86_64.
+        // Non-x86 platforms must use PCIe memory-mapped configuration space.
+        panic!("pcid: PCI 3.0 I/O-port fallback is not supported on this architecture")
     }
 
-    unsafe fn write(&self, addr: PciAddress, offset: u16, value: u32) {
+    unsafe fn write(&self, _addr: PciAddress, _offset: u16, _value: u32) {
         let _guard = self.lock.lock().unwrap();
-        todo!("Pci::CfgAccess::write on this architecture")
+        panic!("pcid: PCI 3.0 I/O-port fallback is not supported on this architecture")
     }
 }

drivers/redoxerd/src/sys.rs

@@ -43,8 +43,8 @@ mod imp {
         }
     }
 
-    pub fn write_debug(b: u8) -> syscall::Result<()> {
-        // TODO
+    pub fn write_debug(_b: u8) -> syscall::Result<()> {
+        // AArch64 debug output is not implemented; silently drop the byte.
         Ok(())
     }
 }
@@ -52,18 +52,14 @@ mod imp {
 #[cfg(target_arch = "riscv64")]
 mod imp {
 
-    pub fn exit(success: bool) {
-        todo!()
-        // let q = qemu_exit::RISCV64::new(addr);
-        // if success {
-        //     q.exit(51)
-        // } else {
-        //     q.exit(53)
-        // }
+    pub fn exit(_success: bool) -> ! {
+        // RISC-V QEMU exit is not enabled for this build; the QEMU exit address
+        // is board-specific and not currently wired.
+        panic!("redoxerd: QEMU exit is not supported on riscv64")
     }
 
-    pub fn write_debug(b: u8) -> syscall::Result<()> {
-        // TODO
+    pub fn write_debug(_b: u8) -> syscall::Result<()> {
+        // RISC-V debug output is not implemented; silently drop the byte.
         Ok(())
     }
 }

drivers/storage/bcm2835-sdhcid/src/sd/mod.rs

@@ -16,8 +16,10 @@ pub(crate) unsafe fn wait_cycles(mut n: usize) {
 
 #[cfg(target_arch = "riscv64")]
 #[inline(always)]
-pub(crate) unsafe fn wait_msec(mut n: usize) {
-    todo!()
+pub(crate) unsafe fn wait_msec(_n: usize) {
+    // The BCM2835 SDHCI driver is Raspberry Pi specific (ARM/AArch64). RISC-V
+    // is not a supported target for this driver; timing is therefore unreachable.
+    panic!("bcm2835-sdhcid: not supported on riscv64");
 }
 
 #[cfg(target_arch = "aarch64")]

drivers/storage/ided/src/main.rs

@@ -299,6 +299,7 @@ fn daemon(daemon: daemon::Daemon, pcid_handle: PciFunctionHandle) -> ! {
 }
 
 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
-fn daemon(daemon: daemon::Daemon, pcid_handle: PciFunctionHandle) -> ! {
-    unimplemented!()
+fn daemon(_daemon: daemon::Daemon, _pcid_handle: PciFunctionHandle) -> ! {
+    // IDE is an x86/x86_64 legacy controller; no other architectures are supported.
+    panic!("ided: only supported on x86 and x86_64");
 }