ahci: skip ATAPI ports and fast-fail on device abort

A CD-ROM (or any ATAPI device) on a scanned port previously made the
driver spin the full 100M-iteration timeout on IDENTIFY, then log a
scary 'timed out' (QEMU leaves ATAPI aborts pending in PxCI instead of
completing the slot; tfd=0x441 = ABRT).

- skip a port up-front when firmware set PxCMD.ATAPI (bit 24)
- bail out of the completion poll as soon as PxTFD.ERR is set, clear
  the error bits and any wedged slot, and report the abort instead of
  timing out — the port scan stays fast with a CD attached

1 files changed, 22 insertions, 5 deletions

diff --git a/rsnix/src/ahci.rs b/rsnix/src/ahci.rs
index ea1a886..2efe3b4 100644
--- a/rsnix/src/ahci.rs
+++ b/rsnix/src/ahci.rs
@@ -165,6 +165,13 @@ fn start_port(abar: usize, port_idx: u32) -> Option<Disk> {
     wreg(port + P_CMD, CMD_FRE | CMD_SUD | CMD_DMAE);
     wreg(port + P_CMD, CMD_ST | CMD_FRE | CMD_SUD | CMD_DMAE);
 
+    // ATAPI (optical) devices reject ATA IDENTIFY — skip them so the
+    // scan doesn't waste a timeout on a CD-ROM.
+    if reg(port + P_CMD) & (1 << 24) != 0 {
+        crate::serial_println!("ahci: port {}: ATAPI (optical) device, skipping", port_idx);
+        return None;
+    }
+
     let mut d = Disk {
         port,
         clb,
@@ -175,7 +182,7 @@ fn start_port(abar: usize, port_idx: u32) -> Option<Disk> {
     };
     // IDENTIFY DEVICE as a sanity check + to learn the capacity.
     if issue(&d, ATA_IDENTIFY, 0, 1, false).is_err() {
-        crate::serial_println!("ahci: IDENTIFY failed on port {}", port_idx);
+        crate::serial_println!("ahci: IDENTIFY failed on port {} (not an ATA disk?)", port_idx);
         return None;
     }
     let id = unsafe { core::slice::from_raw_parts(d.buf as *const u16, 256) };
@@ -333,13 +340,20 @@ fn issue(d: &Disk, cmd: u8, lba: u64, count: u32, write: bool) -> Result<(), ()>
         *hdr.add(3) = 0;
     }
 
-    // Issue and poll.
+    // Issue and poll.  Bail out as soon as the device reports an error
+    // (QEMU leaves ATAPI aborts pending in PxCI rather than completing
+    // the slot, so we must not wait for the timeout on those).
     wreg(d.port + P_CI, 1);
     let mut i = 0;
     while reg(d.port + P_CI) & 1 != 0 && i < 100_000_000 {
+        if reg(d.port + P_TFD) & 1 != 0 {
+            break;
+        }
         i += 1;
     }
-    if reg(d.port + P_CI) & 1 != 0 {
+    let tfd = reg(d.port + P_TFD);
+    let tfd_err = tfd & 1 != 0;
+    if reg(d.port + P_CI) & 1 != 0 && !tfd_err {
         crate::serial_println!(
             "ahci: command {:#x} lba={} cnt={} timed out (tfd={:#x} ci={:#x} cmd={:#x} prdbc={:#x})",
             cmd,
@@ -352,9 +366,12 @@ fn issue(d: &Disk, cmd: u8, lba: u64, count: u32, write: bool) -> Result<(), ()>
         );
         return Err(());
     }
-    // Error?  Clear any port error bits either way.
-    if reg(d.port + P_TFD) & 1 != 0 {
+    if tfd_err {
+        // Clear the error bits and any wedged slot so the port stays usable.
         wreg(d.port + 0x30, 0xFFFF_FFFF); // PxSERR: clear
+        if reg(d.port + P_CI) & 1 != 0 {
+            wreg(d.port + P_CI, 1);
+        }
         crate::serial_println!(
             "ahci: command {:#x} error (tfd={:#x})",
             cmd,